Robin is very smart, but he seems to have some difficulty translating what he knows into the right word coming out his mouth. This is true about colors, and letters, and numbers, all of which he basically knows, but all of which he has a hard time spitting out the word for in the moment.
Just this week he seems to be beginning to be able to smoothly start counting at 1 and get all the way through to 10 without stopping in the middle. I'd say he's about 75% doing that right now.
I've wondered and wondered if he might be colorblind (my grandfather and one brother are red/green colorblind) but last week when we were in the doctor's office they happened to have a book of colorblind tests sitting there and I asked him to look at it. He couldn't say the numbers they were using (like, 73 and 124) but he traced them with his fingers - he definitely could see them (which he couldn't if he were colorblind).
And we keep working on letters. Some he's quite clear on - others he has to guess the names for (but he gets them about 90% right if I give him multiple choices.)