Well, the short answer is: It doesn't matter
If that's all you need to know, feel free to go and buy your favourite colour filament for your next project. For a more nuanced answer.... read on
What Colour Do I Use?
I generally print my miniatures in grey filament.
Why?
Because it's a neutral colour, so when I'm priming my miniatures in black and/or white I can see which bits I've missed really easily