Assuming you're learning ASL, the colors are pretty easy since a lot of them are initialized, meaning they use the handscape for the first letter of their English name in the sign(yellow, purple, green, blue) and they use the same basic motion. You may find this site helpful. http://aslbrowser.commtechlab.msu.edu/browser.htm

There are a lot of great online resources for ASL, but the one I use the most is www.handspeak.com. As far as learning colors or any other specific type of vocabulary I recommend learning them in context. For example: Black cat or orange juice is easier to remember than a list of only the colors. Have fun!