How old was your child when they understood colours? My youngest child is 25 months. He can colour match - i.e. add a red brick to a tower of red bricks - so he's not colour blind. But if I say pass me the red brick, or what colour is the post box, he hasn't a clue. My eldest child could do this sort of thing when he was 18 months. I have no idea which of them is more normal, and whether we should be worrying about the little one. (He also mixes up other words in categories - i.e. regularly confuses different animals, and calls members of one family by any of their names. He also took a long time even to work out mummy and daddy consistently correctly.)
Sorry if I sound paranoid. We spent 2 years being reassured that my eldest son's pronunciation problems would sort themselves out, in due course. This didn't happen, and he is now having intensive speech therapy - which is going very well.