[ He's actually listening intently because he didn't know this and it actually fascinates him? There's so much they don't know about their dad and what he actually does, just purely because they took for granted having a god for a parent and never thought to ask about this sort of this thing once they got of their "why" phase. Which he's realizing now is a bit of a shame.

He's surprised with his dad's offer though ]

A-A-Are you sure?! You don't have to do something like that...! B-Blue works fine...!

[ He looks back at this materials ]

I just... suddenly thought about it... because I think she really likes red. But she also has these beautiful green eyes, and I'M green so...

[ And there's that red face again ]