Are you talking about the shift-lmb blur feature? If so, I believe that feature works at a lower bit depth and can't pick up extremely subtle texture variations (such as what's shown in your example image, I can only barely tell it's not a solid color). I'd recommend asking on the official 3D-Coat forums.
I can see absolutely nothing on that picture. Please post a screenshot of your object, your UV layout, and paintstrokes that are distinguishable from the background.
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