What are the differences between the different colors of curry?  

I have not cooked with curry. At least not that I remember. I probably have, but I would have to go check. I may have some Thai curry paste of one color or another. Curry is not an individual spice, but it is a combination of spices, so if you look on different brands of curry powder it will list different things. The main one or one of the main ones is tumeric, which is a bright yellow. It is also called cucurmin. Curries would be good for your ongoing pain issues as tumeric is one of the natural pain relieving remedies for arthritis. It gives many things a golden yellow color.

I think...since it is more forgivable to make mistakes that way that the curry colors are as follows:

Green...hottest-good for chicken or fish
Red.....next in line (my favorite)- nice with pork
Yellow..mild - great for veggies
Orange (yellow with added sour fruit) sour...good for fish

Hope this helps you a bit!