Lily loves wearing pink. Hugo doesn't know why. It might be because she looks good in pink, but then again he thinks she looks good in every colour. He decides it's because she's a girl and girls are a bit odd. This also explains why she likes him in pink, but unfortunately doesn't explains why he wears pink for her (pink shirts, pink t-shirts, pink polo shirts, pink vests, pink jumpers, pink cardigans, pink jackets, pink trousers, pink swimming trunks, pink pyjamas, pink robes, a pink cloak, a pink coat, pink hats, pink gloves, pink scarves, pink handkerchiefs, pink trainers, even pink socks under his black school robes), he after all isn't odd.
It's not even that it makes him feel unmanly, a real man can pull off pink and everyone, even his father (grudgingly), admits he pulls off macho pink. He'd just kind of like to know why she does it and more importantly how she has this power to make him obey.
Most of the school, from the headmistress to the Fat Friar, from Uncle Neville to the house-elf, from their cousin Molly to the other first years, has of course known sine their sorting: PROPERTY OF LILY LUNA POTTER! HANDS OFF!