http://www.vifishandwildlife.com/Edu.../20Treeboa.pdf
I think this is your snake, and it's not a rainbow. Check your endangered species laws. You might not be able to keep it. It looks like a lot like this one, A Virgin Islands Boa. They are native to Puerto Rico.
http://www.bkcave.com/PR/1-8/MiddleA...tana.boa.1.jpg
Last link is thanks to Smulkin.