Ok guys so ive looked around and i cant info anywhere on this problem. Im polypainting onto an .obj file that has uv mapping already applied to it and ive done a great deal of polypainting to the model already, but now suddenly in the middle of polypainting with say for instance the color purple, even with that color selected in the color picker, zbrush will polypaint a dark pink, or a red color instead of the color i have picked. i even tried selecting both foreground and background colors as the color i want, ive tried painting in fast reender mode and also on a flat color material. i dont understand, why isnt zbrush coloring the color i want? it seems to work fine when i first open zbrush but after painting for a bit, without changing any options at all, it starts to color a different color altogether. wtf? please help asap? 
little help please? : /
Check that the Brush>Alpha and Texture>Polypaint Mode is set to 1.
I checked and it is set to 1. I started with a fresh load of zbrush and began painting on the model. I clicked “c” on the model to grab a color from it and everything was working fine but as soon as i did color grab again the color that was selected was blue but it started painting red. scratches head i dont understand :(. btw i was wondering if there is any way to export the uv map from a model with the polyframe on it?
I’ve no further suggestions on the color behaviour. I’ve no idea what’s going wrong.
If you press Tool>Texture Map>New from UV Check when polyframes are showing on the model (hotkey Shift+F) then the resulting map will show the polyframe.
thank you. 
the color picker in zbrush4 is just a mesh. it will pick the right color but the color palette will show you something else. I can’t believe there is no official answer and no fix for this in the latest release. Really frustrating!!