Grey is a good choice Blade … that way you can fire a flash onto it, turning it white, or you can underexpose it, turning it nearly black, you also have the option of gelling your flash on the backdrop to create coloured backgrounds …
Colours introduce the difficulty of ensuring your subjects clothing, makeup and styling don’t clash with what colour background you use. My recommendation would be a neutral grey which gives you a huge amount of flexibility and is neutral, so shouldn’t detract attention from the subject.