Percy disliks the colour red.
It held connotations of Weasleys, Christmas, Gryffindor and Weasleys. In turn, Weasleys held connotations of teasing siblings and uncomfortable hugs, and both Christmas and Gryffindor held connotations of Weasleys.
But when Percy watches Oliver bullet through the air, in regal, red quidditch gear, he finds he had a lot less to dislike about the colour red.
Oliver is enchanted by red.
His house's tower, quaffles and the water from the third tap in the Prefects' bathroom are all wonderfully, unmistakably red. His blankets were red, strawberries were red and he liked to write essays and letters in thick, gloopy red ink. He had a feeling it had something to do with the (red) flush that frequented his (red-headed) dorm mate's face.
But when Oliver watches Penelope Clearwater stutter and glow a vivid, bright red when talking to Percy, he finds he is a lot less enchanted by the colour red. By that shade at least.