If you don't want any lighter areas, don't use any fur texture at all on your mane. The body and tail should be fine.
As for the mouth area, make sure you haven't used a soft eraser tool, make sure the eraser tool you use is a sharp edged one. The smoother eraser tools appear to cause issues for people, such as this situation here.
Moving to Game Help.
Also check the preset coding for your head. You may have it to reflect light or something to that affect.
It seems your preset has an ambient affect added to its material file, causing it to have a "reflecting" appearance. The transparency code you used must have included some extra additions. If you'd like, I can look over your .material file or get you a new transparency script (without other effects).