That's just polypaint. You probably have the alternate button enabled (Color: Alternate), which means if you hold alt it will also use the secondary polypaint color (in this case, black). Turn off RGB, or switch off alternate, or set both colors to white.
Inactive Subtool Dimming. Turning on polypaint will show the subtool at it's full brightness, as would rendering with BPR. Or you could go into your preferences and adjust the dimming value (under Pref: Edit). It goes without saying to also make sure they're using the same matcap, and that the noise setting didn't have the…
When the noise is not applied, it's not really displacing the actual geometry and it isn't dependent on the vertex density of the model (slap some noise on a basic cube and it will still look nice and crisp). It might be better to turn off the strength of the noise and use the color blending only to create a polypaint…
Just reset the polypaint-material info (fill it with flatcolor) and clear any masks on the subtools. As for the polygroup, only create them on the lowest subdivision level. Otherwise if you open the tool again or step down in subdivision levels, then they're going to get re-evaluated from the ground up (which will create…
Are you sure you haven't filled your object with a material ('M' button or 'MRGB' buttons selected)? Cryrid suggested doing a fill with flat color (to remove the 'm' data which could be baked in but if you fill without either of those buttons toggled it probably wont remove the baked mat (if there is any). As Cryrid also…