If you could have only one?
Grey.
Why grey?
Because it can do almost anything. It is the fascilitator, the giver and the balancer.
Too much?
Point taken, texture ignored.
Grey, plain and boring, is the best because it can be all you want within limits, but you have to work for it. As is, it is pretty drab, only suitable for a few subjects, but with some effort you can;
Darken it to darker grey or even black by starving it of light,
lighten it to as light as white, by blitzing it with more light than the subject,
shift its colour using post processing, quite easily with brush tools or even just white balance,
use it as a colour bleed-proof replacement layer, like an optional green screen,
vignette it,
simply use its neutrality to hold the subject in stark relief,
change its overall colour completely or shape it using gels on strobes,
use it as a neutral starting point for white balance and exposure.
*
Black is limited because it can do most of this, but needs more light pushed into it and sometimes the flatness is sacrificed for saturation.
White is similarly limited as it is harder to get a balanced grey out of in the first place, effectively making some actions a two step process.
Textures are also limited, because you tend to need more than one or everyone will notice your images all look the same.
The Lastolite I have coming is hopefully an ideal example of the above, with black as an option.