Okay, these aren't free, but I've been using these and think they are a great resource for the price. For the low subscription fee ($20 per year) to Enchanted Learning, you have access to a wide variety (tons) of printable educational materials.
I use the color word books I'm listing here for teaching many different skills: vocabulary development, colors, color words, reading, writing, etc. There is a lot you can do with these materials, and I've been using them for about 4 of my students with autism. I think they are structued in a way that is very clear and non-distracting, which is good for my students.
Here's the list: