Ok on the template the face is 3.27 times larger than the body. So if you leave your photos the same size your body will look to be much lower res than your face. This will cause color difference when it gets mapped to the figure. It will also cause a seam even if the color matches. IMHO that this was done for the sole purpose of keeping just anyone from being able to texture, LOL, keeping compitition down. As to how to get around it you would just have to scale your photos for the head and face according to the ratio for a better resolution match.

I may be wrong and someone will tell me if I am, but I believe this is what causes the color difference.