Paint would be fine if you did it without the snake in it, of course, and gave it plenty of time to dry. And painted the outside only, of course.
Another option that I've done is just picked up some black construction paper or poster board and cut it to size and taped it on the outside. That made for a nice dark background and helped the snake and interior elements pop.
Or you can do like my daughters did and buy these Background Clings and stick them on the outside:
http://www.petsmart.com/reptile/habi...6-catid-500027
They make their tanks look cool.
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