FMR is the biggest offender when it comes to forcing crabs into painted shells. We are working on them too but if stores would stop buying the crabs in the painted shells, it would probably have a bigger impact. Hermit crabs will rarely move into a painted shell voluntarily. As you can see, there is risk of them getting trapped in the shell when it is too small and the paint is not dry.
I mean, really, you wouldn’t dream of dyeing other pets different colors would you? So why subject the crabs to it?