Hi A.,
I wondered if my son was color blind too! Turns out, he's not. I was frustrated that despite how much we tried, he was not "getting it". I began teaching him around 2. I'd use color words in my daily talk. Example: "It's time for breakfast, let's get the yellow box of Cheerios." "Today you're going to wear this blue baseball shirt." We also worked on puzzles and read books with color words. He'd repeat what I said, but when I "quizzed" him, he was rarely correct. Around 2 years, 2 months, we began potty training. Every time he was successful he got some M&Ms. Since they are all different colors, that was a great tool to practice with... let's put all the green ones in a pile... now all the red, blue, etc. He was able to correctly put the colors together (which made me believe that he could distinguish the colors, but did not recall the names). Then one day, my husband had about 10 M&Ms in a little bowl. He told our son to pick a certain color "Pick the yellow one." And to my amazement, he was correct every single time. I then realized that he knew his colors, but did not master them! So, from then on I'd give him the name (much easier than having him try to recall a color word). So, I'd say "Please go find a toy that is blue." And to my surprise, he'd normally come back with the correct one. However, if I tried to do it backwards, where I'd get a toy and ask him the color... he hardly ever knew the name. So, start with that. Give him the color word. Keep practicing in fun ways. Use color words in your daily language. Before you know it, he'll be learning them!!
Hope this helps.