I personally find it better to create eyebrows separate from the original texture and put them in place after the fact. This way you can scale and bend them in the desired shape I create ever thing fist in gray scale first by hand so this does not necessary apply here with your project. But working in gray scale (changing any photographic elements) first will give you the options of creating any skin or eyebrow hues, shades, tones, or tints you desire. More over it is easier to blend the UV map seams in gray scale The average human can only detect 250 hues - but can detect along with and in combination, 350 variations of gray (black through to white). Meaning your eyes are more in tuned to seeing and picking up gray than color. The image I posted above is of my Vista V3 Character and she was created with the methods I spoke of above. She was all created in gray scale first and was tinted with color blend options after the fact.