There's nothing inherently wrong with black rubber/EPDM for a roof; the vast majority of them are black. The only downside is that the dark color absorbs much more heat from the sun than lighter colors.
Not generally an issue with residential roofing with a traditional attic space, but a camper doesn't have that and would tend to get pretty toasty inside with no effective means of passively removing that heat. Having said that, there are white/light-colored coatings you can apply to alleviate that concern. The time and cost associated with that might make spending a bit more on white rubber a little more palatable.