What on earth is this? showed up while I was polypainting my object. Once I pressed on Grd in the polypaint menue it fixed the problem. But today as I started up zbrush again the strange pixel artifacts are back.
What are they and how do I get rid of them??
I believe Grd should be on by default before you start to polypaint. To fix it you can turn on Mrgb, select the material, then go to ‘Color’ menu and FillObject
Note: This will cause you to lose any polypainting you did on the subtool.
thankyou 
That fixed the problem, really thanks a bunch