If you want a colorful tortoise, then BUY one. Do not paint a Baby tortoise's shell with craft paint or let your kids paint the shell with fingernail polish.
It is extremely toxic and will make the tortoise sickly and/or die.
See poor Derp's shell? After a half dozen scrubbings, she's still got toxic fingernail polish stuck to her shell. :(
Derp, Pancake, and Tiny Tim all came to me with painted shells. :( Please don't.