For certain colors, it is common to change with maturity. For example, many agouti colors (including chin, like your bunny) will change over time a bit. Shadeds tend to also. It usually happens around the time they get their adult coats in.
My buns changed a lot in there first year. Tobias is a broken orange...and he went from being white and VERY VERY orange to white and reddish-brown. Balthazar changed back and forth several times...as a harlequin, he started out white and dark grey, and then a lot of his grey went almost white...and then it darkened again. I'm assuming it's a seasonal thing, so it could happen again.