A/N: This one-shot is an AU based on the Tumblr post about an AU where the world is black and white until you meet your soulmate, and returns to black and white if they die.
"I wish you could see the colours," John sighed, gazing out the window. Sherlock didn't reply, just remained stretched out on the sofa, hands steepled, eyes shut. "The first time I saw Mary blush..."
"Honestly John! I've read your poetry, I don't need to hear you waxing lyrical now," Sherlock grumbled, reluctantly shifting from the sofa, and standing next to John staring out of the window. "I don't see what all the fuss is about, I can make all the necessary observations without colours."
"Just because you're married to your work doesn't mean we all are. Look, I've, well I've been thinking about it a lot, and I'm going to propose to Mary. This just proves that we're meant for each other."
"What does?" Sherlock replied, confused.
"The colours, idiot! And don't you have anything else to say? I've just told you I'm going to propose!"
"I suppose good luck. She will say yes though, so on second thoughts, congratulations." As John spluttered, a buzz signalled that Sherlock had a message.
"Lestrade needs us at St Bart's, there's been a murder," Sherlock said, grabbing his Belstaff. "Coming?"
"Yeah alright you git," John moaned, although he was secretly relieved to know that his proposal would be a success.
Arriving at St Bart's, Sherlock strode into the morgue, coat billowing behind him, and then came to an abrupt halt. An unfamiliar woman stood with her back to him, hair tied back in a ponytail, a lab coat over a rather frumpy ensemble.
"Who's this?" Sherlock demanded of Lestrade. As the woman turned around, looking rather embarrassed, Lestrade stepped in.
"Manners mate! This is Dr Molly Hooper, the new pathologist. Dr Hooper, this is Sherlock Holmes, consulting detective."
"Oh, um, hello, call me Molly," the woman stuttered, extending a hand. As theirs eyes met, Sherlock almost recoiled, as he saw two, rather beautiful, brown eyes looking into his own. If he hadn't been so shocked himself, he would have noticed her rather similar reaction. Instead, he composed himself and coolly replied, "Sherlock, this is John Watson. Can we get on with this examination, I'm rather busy?"
He immediately regretted his actions as the small woman before him burst into tears and fled the room. "What the hell?" Lestrade exclaimed. "I know you're not the friendliest, but that was a bit of an overreaction."
"Nothing happened!" Sherlock exclaimed rather too quickly, stalking over to the body. After a quick glance, he rapidly spoke. "It was the son, he had cut him out of his will. Now if you'll excuse me."
And with that, Sherlock stormed out of the morgue, leaving John to apologise before dashing after him. There was no sign of Sherlock anywhere, so John caught a cab back to Baker Street, where the sound of violin music greeted him as he opened the door. "Sherlock?" he called out cautiously, entering the flat slowly. "What was that all about?"
His flatmate spun around, eyes wide. "Colours!" Confusion clouded John's features, until what Sherlock had said registered fully, and he almost choked for the second time that day. "You mean she, you know, Molly Hooper, is your...soulmate?"
"I don't know! I thought that it was all irrelevant, but then I saw, well I saw her, and the colours John! Her hair, the way she blushed, she's beautiful!"
"Whoa, slow down mate, calm," John said, putting a hand on his friend's arm. "You need to go see her, apologise, maybe sort out a date."
"What? I don't do emotions!" Sherlock yelled, and John could have sworn he rolled his eyes. "How am I supposed to confront her? She might not have experienced the same..."
"Mate, anyone with eyes could see that she felt the same way, now go get her!" John exclaimed exasperatedly, practically shoving Sherlock out the door.
And so it was that half an hour later, Sherlock was back at St Bart's, searching for Dr Molly Hooper. But she was nowhere to be found. Still overwhelmed by the vivid colours, Sherlock sat for a moment, gathering himself and deciding on a course of action.
"I'll ask the receptionist," he thought, standing. Just as he was about to approach the front desk, a wave of nausea passed through him, as he realised that the colours were fading. The daffodils arranged in a vase on the desk, previously a sunny, cheerful yellow were now a sickly, pale colour that more closely resembled the pallor of a dying man.
A surge of panic overcame him, and he rushed to the desk. "The colours, they're, they're fading! What's wrong?" he shouted, gripping the desk so tightly that his knuckles were white. The receptionists smile fell, an unmistakeable look of sympathy showing instead.
"Calm down sir, just take a seat and I'll fetch one of the nurses," she said, knowing only too well what was wrong, but unwilling to tell him.
As he realised what it meant, yelling her name, the doors of the hospital flew open, and an emergency team rushed through, pushing a stretcher. The sight filled Sherlock with horror, as he recognised Molly Hooper's delicate frame, confirming his fears. Again, he shouted, "Molly!" running towards her, only to be restrained by two nurses, a sudden jab causing everything to fade to darkness.
"Molly," Sherlock murmured, eyes shut.
"Sherlock, can you hear me?" John said from the bedside, waiting for his friend to come to.
"Molly," he muttered again, this time more loudly. Then, his eyes flickered open.
Everything was black and white, no longer full of colour. As the realisation hit him, Sherlock took a deep breath, before slowly breaking down into sobs, shutting his eyes as if that would change what had happened.
Later, everything was explained. Molly, distraught at finally discovering her soulmate, only to be dismissed, had fled the hospital, and whilst distracted, stepped into the path of an oncoming cab, causing her death.
Sherlock Holmes was once again alone, in a world of black and white. His only acknowledgement of the brief period of colour in his life was the bunch of daffodils he placed at her headstone each year, a reminder of the colours that could be washed away as quickly as they appeared.
A/N: Sorry! I'm not even in a bad mood, just felt like writing something after seeing the prompt! Reviews appreciated :)