Harry's eyes are grey, when he's sad. It's not quite that strange at first, not too noticeable- children's eye colour changes all the time when they're younger.
When he's eleven, his eyes flash a festive, bright yellow with his happiness, light orange flaring at the edges to create a stunning golden colour.
(Sometimes, when he's happy, his hair changes too. Often quiet soft cloud white will appear at the fringes, when it's a calm happy. When he's satisfied and relaxed, the soft black curls turn the gentle red waves of his mother in his relief. The frenetic mania of stress or of finally finishing something turns his hair to pink.)
In the wizarding world, he's a metamorphmagus. In the mugfle world, he's just someone who has light sensitive eyes. (In the muggle world, he's always suppresses that bit of himself.)
Lucius leans forward to kiss him the first time, and the soft glow of orange-yellow makes him smile. He sculpts around Harry's jaw with his hand, gently cupping his cheek and looking him in the orange eyes.
"You're beautiful," He says, both because it's true and because he's not blind.
(Someone, soon to be nothing but a gravestone, has made Harry feel alienated for himself. It makes him infuriated, to see him trying to shut down what shows that he's happy.)
"And if you haven't been told that from your very first days, someone has done you a disservice."