The theory I'm going with in SoG/TGZ is that Saguru does have some colour blindness, because of that suit. Yeah, we know, mean of us, but it just felt right for that fic.
Have a friend I've been talking to who has colour blindness and it's like you were saying about your father. Only to him some colours look the same, or when looking at a graident, it'll be one solid colour, then another solid colour, none of the shades in between.

Hm... the purple sock could belong to Mum!!!
(and it's not nearly as bad as all-argyle socks. Although I'm amassing a collection of them in RL)