Ciao,
Thanks for that info. Yeah, after a couple of hours of fooling around with SpotLight, I’m getting the hang of it as well. Its such a powerful feature I wanted to make sure I would be able to use it. When Pixologic shows off their features its so exciting, and you just want to be able to do what they showed. For instance, cutting out a portion of a picture. In the video they showed parts of the image painted in red and then magically the red became transparent and they could cut out a door or window. So, I tried the same it took me a while to figure out how to change the red into a transparent area. (make sure that one of your colors is pure black 0,0,0 and then place your cursor over the area (red paint) that you want to replace with pure black (transparent) hold the Ctrl down and dial your paint widget positive if black is your primary color, or negative if black is your secondary color. Your red area becomes transparent.) A clear tutorial would show these features. But, I guess discovery is part of the challenge.
Gary
I am having the same trouble with spotlight. Objects with uvs done in uv master wont paint. Other objects do (ie no uvs). If you cant use paint with spotlight, try to just paint a stoke on your model, bet you cant.
As usual it will be one button, so I will put the answer here when I have it.
Check that you don’t have a texture on your model. If you do, you won’t be able to paint color through Spotlight.
Yep, that was it. Switched texture off and it is working. Thanks man. I knew it would be one button ha ha.
Yeah, but one button out of so many… 
Glad that fixed it. 
The thing I like least about zbrush are those Doh! moments, where you simply cant blame the software :D.
Just to add an extra 2-cents… There’s a Spotlight basics video on You Tube …