What color is this Puppy?

Is she still with the litter or has she recently been separated?  If recently separated, the first thing I would check is diet.  Copper deficiencies can cause this kind of reddish color in the coat.  

If diet can be ruled out then she is probably just a variation of black alot like some horses are black, but not quite black.  No one knows what causes these differences.   

Here is a thread on seal pitpulls that you might find interesting. 
http://colorgenetics.info/color-term-seal

And other thread that might be relevant 

http://colorgenetics.info/forum/canine/canine-color-genetics/interesting-belgian-groenendael-puppy

Thank you! No she is still with the litter, and you could see from the first day on that she is not normal black, like some of her brothers and sisters. Maybe a very intense red? I add a photo of her mother And her grandmother, she is the blue merle) and try to make new Photos of this little girl the coming week. The PhotosI have posted are a few weeks old, now the brown is more visible.

Here are Photos of the little Girl from yesterday ;)

I do believe this would be called "seal" in pitbull circles.   It does appear to be a light form of dominant black.  What actually causes the difference?  I don't have any idea.  It could be something like what causes the difference between highly expressed or minimally expressed black and tan.  

I do find it interesting that she appears to have "light areas" in the same general location as brown/seal horses.  This can safely be added to the "things that makes you go ???" category.  

UC Davis and Animal Genetics offer tests for Dominant Black and Agouti.   I would love to see the test results.