I’m not sure if anyone posted this before, on the ZBrush home forum I’d be surprised if it hasn’t. Anyway, I always have problems trying to decide what is a good skin colour to pick. By accident I found that if I load a texture with the skin colour I want, I can hover my cursor over the texture thumbnail, click C and pick up the colour without ever having to bring the texture into the main window. You need to then turn texture OFF to paint only with the picked-up colour.
I made a short video, it might help someone.
Almost forgot to mention about the video, nudity/nipple alert.