I think this is a one shot, but I'm not entirely sure. There's a guy who's raising a kid (possibly a teenager? Again, not sure >.<) and the kid thinks that this guy is a friend of the deceased mom. But it turns out that the guy is actually the kid's father, and he changed his appearance to keep his identity a secret because the mom's parents didn't approve of their relationship and they didn't want the kid to know anything about the father. I think the colour of the dad's eyes is key somehow because the kid figures things out when he/she accidentally sees the dad w/out his contact lenses. Does this sound familar to anyone?

It's a one-shot called Hana and Ageha, the summer from Shiawase Kissa 3-choume.
(It's in vol.4)

That's the one! Thank you so much! =)