This one is pretty gentle compared to potentially life-threatening things but still interesting. Not seeing colour can actually make things pretty difficult.
Characters:
Colourblind!Percy / Colorblind!Percy (UK v US)
Grover (the sweet forgotten summer child)
Leo / depressed!Leo (but tbh that's just canon)
Annabeth (of course)
Will (Doctor man to the rescue)
Brief appearances:
Hazel
Frank
OC daughter of Iris
Lightning Thief:
"What kind of punishment is picking strawberries, anyway? I'd rather clean the toilets again," Percy huffed.
"Hey! Some people actually do this for fun, you know. Like me." Grover trotted pantslless in front of Percy, going backwards with little jumps to look at him.
"Like how some people get beaten up by Clarisse for fun, right?" He kicked the ground, looking at his feet.
"You're just in a bad mood."
"I know!" Percy snapped as they arrived at the fields.
"Only pick the red ones," Grover advised and leaped over a bush that Percy would be working on the other side of.
Percy was silent. He looked at the strawberries. Some were lighter than others, maybe, but if experience had taught him anything it was that red and green must be almost exactly the same colour, because as far as he could tell, they were the same shade.
"How can you tell which ones are red?" Percy asked after Grover had already entered the zone and begun picking and happily whistling. The satyr paused.
"What do you mean? They're red." He placed a strawberry that Percy assumed was red into the basket on Percy's side of the bush. "Red."
Percy blinked at it, then frowned at the bush. Leafs are green, unripe things are green, ripe strawberries are red. But the whole bush looked the same freaking colour. He took his best guess and pulled one from the bunch.
Grover looked over initially annoyed, then frowned in consideration. "Are you colour blind?"
"Duh. I thought you already knew that."
Grover scrunched his face together and looked with some longing at the fields of grey Percy couldn't quite understand his attraction to. "Maybe we can find you something else to do that doesn't have to do with differentiating between red and green."
Percy frowned. "It's other colours, too."
"So you're not red-green colour blind?"
He shook his head. "I'm completely colour blind. Which means I don't see colour. Everyone could suddenly turn purple and I wouldn't notice. Well, no, depends on the shade, I guess... Like violet or... I dunno, what are other names for shades of purple?"
Grover knew when to ignore tangents. "Do you know what colour shirt you're wearing?"
Percy looked down at his fluorescent orange camp shirt and considered it. "Hmmm... probably not green... Blue?
"It's orange."
"Oh."
"Wait, how is blue your favourite colour if you can't see it?"
"It was the one colour I used to be able to see. Well, I guess actually it was blue and yellow but yellow is just old white. Blue is fancy white. I mean, I could never see them fully, but I have some idea of what they're like. And blue is, like, an act of rebellion. Making food blue. You know that, though."
Grover nodded. "That's kind of... sad."
Percy shrugged and stood up, not bothering to brush the dirt from his knees. "It's not too bad."
"Is that why you didn't want to come out here?"
"Picking strawberries?" Percy clarified, and Grover nodded. "Yeah. I don't like to feel like I have a disability."
"Which is why you never mentioned it?"
"Not until you asked."
"Sorry." Grover picked up the basket with one red and one green berry in it. Percy waved a dismissive hand. "I'll tell Chiron why you can't complete your 'punishment' and see if you can get off free."
"Mr. D would never let that happen, but you can go ahead and try. Thanks, by the way."
"No problem."
Mark of Athena
Leo fiddled with some gadget he was making at the table. Percy wan't out on the deck guarding, which meant he should be sleeping, in theory, but he couldn't bring himself to lie down. Leo's tools were sprawled across the length of the dining table, him on one end and Percy on the other, and neither boy had said anything since they both sat down. Percy's eyes were closed despite his refusal to sleep, and he was enjoying the feeling of being over water.
"Jackson, you asleep?" Leo whispered in the loud kind of way that it would have woken Percy up if he had been asleep.
"Nope," He said, eyes still closed, head leaned back so that the pressure of his neck against his Adam's apple made it difficult to speak in anything but a smothered, low tone.
"Could you toss over the yellowish plastic in front of you?"
Percy opened his eyes and looked out of the bottom of them only to find that there were at least eight different sheets of plastic ranging in thickness, shape, and shade of grey. "Don't you have tool-kinesis or something?"
"No. I also don't have my yellow plastic." Leo barely bothered to glance up. He seemed in bad mood, which was unlike him in general, and Percy didn't want to make it worse.
"Right. The yellow one." He sat up and surveyed the table as quickly as he could. Yellow was light, right? So just the lightest one. That was fine. He chose one that looked almost white and threw it to Leo. The son of Hephaestus looked up while reaching for it, then paused with his hand just above it. He looked at Percy.
"Either you hate me, you're completely colour blind, or both."
"Why do you have so much plastic all over the table anyway?"
"So both. The yellow one is on your far right."
Percy hit the correct yellow sheet of plastic over to Leo, mildly embarrassed, impressed at Leo's fast guess, but mostly disappointed in himself. He had been able to guess just fine until today.
"I don't hate you," Percy said.
Leo chuckled in a way that scared Percy a little. "I know. Only I do that."
Percy was silent. So was Leo.
"How about," Leo proposed in a too-serious tone, "I don't tell people you can't tell an apple from an orange, and you don't mention my bad day?"
"Apples and oranges have different shapes..."
"Percy."
"Deal."
Leo nodded to the older boy and continued with his strange, yellow project.
A little while passed before Leo took in the 'before I speak' breath and Percy opened his eyes again. "You should probably tell everyone before something happens and it becomes a real problem."
Percy looked defensively into Leo's dark eyes. "Right back at you."
Some made up event taking place some time in Heroes of Olympus but after that last scene:
"Red wire to the blue godsdamn circle."
Percy could hear that Leo was beyond annoyed through the blockade as he stared at the monochrome control panel.
"I can't," Percy stared desperately like maybe if he didn't blink some colour would return to his world.
"Why not!?" Annabeth called, pacing as the second baracade, this one with thin spikes attached, closed in with agonising slowness.
"I'm colour blind," Percy whimpered in utter frustration, "Completely."
Annabeth was silent.
"Wise Girl?"
"If I had known that I wouldn't have pushed you into the control room," Annabeth said, barely audible.
"Now isn't the time for I-told-you-so's... but I told you so," Leo said.
"We'll find a way around it. That's the biggest problem right now."
"Chica, I think the biggest problem is that we're going to become demigod kebabs," Leo's voice was somehow devoid of panic.
"Right."
"I can kinda see some different shades... but all of the connectors are circles, so that might be a problem," Percy brought them back to task, feeling more useless than ever. Less than useless; a weight dragging everyone down.
"Okay, alright," Leo gathered himself, "There are two red wires. The one you need can only reach one blue circle. It's light blue so if there are any really dark ones rule them out. If a wire can reach two or more light circles, rule them out."
Percy took a deep breath and did his best to identify what Leo had said. There were a few dark circles. Nope. There were some wires that didn't reach light ones at all, not those either, and not the ones that were so long they could reach everything.
"Did you connect anything?" Leo asked quickly.
"No."
"Well, something happened, 'cause the wall is moving faster now. How dark do you generally see... I dunno, an apple?"
"Like medium dark, I think." Percy looked for an apple-shaded wire.
"Rule out any wire significantly lighter or darker that what you imagine," Annabeth cut in.
Percy measured his greyscale. "Two left."
He could hear a loud sigh from through the wall. "Guess."
Nopenopenopenopenope.
Nope.
"Okay."
"And hurry."
His eyes strained trying to see any minute difference that might help decide. One of them was probably green. Why was it always red and green?
He took a breath and reached quickly to the top wire, but stopped before connecting it.
"There has to be another way out," He said instead.
"50/50 chance you save us, just pick," Leo insisted.
"50/50 chance he kills us," Annabeth said.
"We don't necessarily know what will happen if he gets it wrong. It could just speed up again then he does the right one after that."
"We don't even know if he narrowed it down right!"
The wall next to the metal barrier exploded. Percy stood there with his hands out. "Earthquakes."
Leo and Annabeth ran in, and Percy saw behind them the spiked wall closing in far too close for comfort. They hadn't told him to not freak him out, he assumed. Considerate.
Leo looked at the control panel and pulled at his hair in stress. "What were you gonna do?"
Percy went over to that infernal machine and pointed to the wire and connector.
"Do it," Leo said.
Percy touched them. The spiky wall slammed against the barrier.
"That's green and yellow," Annabeth said.
"Damn," Percy breathed. "That would have been... bad."
~~~~later on the Argo II~~~~
"Completely?"
"No colour," Percy confirmed.
"How sad." Hazel frowned.
"Not really," Percy shrugged. "Some shrimp can see millions more colours than humans can. Doesn't make your lame colour vision sad."
"To shrimp it's sad," Leo said.
"So, you just see everything like a black and white movie," Frank said.
Percy blinked and looked around. "There are movies in black and white?"
"Man, the Wizard of Oz must've been a hoot for you." Leo laughed and the others followed.
"...the yellow brick road?" Percy asked.
"No, it starts off in black and white and changes to technicolour," Hazel said.
"'Technicolour,'" Nico smiled a little.
"Oh. No one told me that," Percy said and sighed. "That might be a little sad, actually."
After the war but everything is good and plot doesn't matter:
"You haven't even brought it up until now," Will gave his disappointed Mom look to Percy.
"It didn't seem important." Percy shrugged. "It's just colour."
"It is important. Especially since we have a cure. Want it?"
"Depends," Percy said.
"On...?"
"Are Annabeth's eyes grey?"
"I think so."
"Then I don't need it." Percy nodded finally.
"I think you'll find that grey is a shade and a colour. You're missing one," Will enticed him.
Percy considered. "I'll ask Annabeth."
The next day he was in the Iris cabin, eyes closed, some stranger's hands on his face.
"This seems a little..." Percy searched for the word.
"Stop moving your eyes," the Iris kid said.
"Far fetched?" Will suggested.
"I was gonna say stupid, but far fetched works too."
"If it's so stupid you can have fun with your varying shades of grey," the Iris kid sassed. She removed her hands. "It's conscious activated—temporary for as long as you want it to last. Switch colour on and off just by thinking of what you want to see." She looked at Will. "He's the last one this year. I don't care if they can't see any colour at all."
"He can't."
"Exactly. Last one. And, Percy, you can open your eyes now."
He continued staring at the dark. It was a different kind of dark. Black made out of colour. Cool. Weird, but cool.
He opened his eyes and immediately gasped, eyes wide, and shut them again.
"Woah." He breathed like he was out of breath. He opened his eyes again, everything Back in Black (and white). His eyes felt like he had just stared into the sun and his brain was overwhelmed, head pounding. "Ow."
Will looked around. "Maybe somewhere less... overwhelming than the Iris cabin would be better."
"No, it's fine," Percy insisted and brought the colour back. He could hardly process it. Everything seemed to be screaming and bleeding, but in a good way, and burning through his retinas. He was determined to keep his eyes open, though he squinted against the rainbows that exploded with colours that he wasn't sure he could name on sight. His mind throbbed. "Wow." He found himself breathless, then dizzy, then on the floor, everything returned to greyscale.
"You passed out," Will explained. Percy could fill in the colour of his hair and skin and eyes with his imagination in a dulled form, and he smiled. "That's a good thing?" Will asked with a reasonably confused look.
"I saw colours! I didn't think I would ever know what they look like. Thanks."
"Uh, no problem. Are you alright? Headache? Your pupils are immensely dilated."
"I have a headache but I'm fine." Percy stood up, clenching his teeth to try to distract from the pressure behind his eyes, and walked outside. Will followed him.
"We should slowly expose you to different-"
"Wow! Green!" Percy cut him off, looking around at the grass and trees in awe.
Will sighed and positioned himself next to Percy so he could ease him to the ground if his brain shut down from visual overload again.
"Wow," Percy breathed again and turned to Will.
The doctor frowned and moved his face closer to Percy's in examination. "Your eyes are rainbow. Must be a side effect."
"So I won't ever be able to see what colour my eyes are?"
"There are always pictures."
"Awesome! Where's Annabeth!?" His eyes changed back to bright green with a blink.
"Probably at lunch with everyone else." Will smiled.
"Let's go!" Percy's eyes blinked back to rainbows and he took off for the dining pavilion.