My went in for his first eye appointment at 20 months and everything was just fine. While there my wife asked a few questions on my behalf. One of them was regarding colour vision. Since my son was about 15 months of age, he knew the signs for BLUE, RED, GREEN, YELLOW and could say “black.” However when we quizzed him on the colours of various things around the house, it became clear that he was more or less guessing. If he’d been quizzed before, he would have memorized the colour and would repeat it back.
RED was by far his best and most consistent sign to recall even on novel objects. However, BLUE was a guess as where the majority of the other colours. He’d call out “black” with good success too. I guess that’s a fairly easy one as there aren’t many shades to compete with it.
I guess my experience is telling me that signing colours is a complicated affair. The doctor mentioned that they don’t measure colour vision until age 5. My wife didn’t get a chance to ask why, but it might have something to do with their ever changing eyes or even their ability to perceive colour. I think it’s pretty safe to assume that teaching the signs for colour is a advanced and should be reserved for older children. You never really know if you child somehow has colour blindness (and there are many different types). You’ll never know if your baby is just not signing right or their perception of clours is different from yours. You wouldn’t want to put them through the ringer on colour tests when you aren’t even sure if they can see what you do. If you are adamant in teaching signs, I would say just experiment with them and don’t make a big deal if your toddler gets colours mixed up. Do always gently correct them though, just don’t put too much importance on being right.