I don't really see much difference between the two, if anything the tan doe is a little steeper rumped than the black doe. If you can, find a helper set them up and take a pic from the side, rear and front. It could be the black doe is narrower and maybe not as high and wide in the escutcheon as the tan doe. Also there are things about a doe that the judge can feel that we can't see, such as the width between her ribs, how soft her skin is, etc.
To help you learn more about showing, I would also look up the ADGA scorecard on the ADGA website. It will tell you how many points are given for each category which can help you know which areas are given the most points and which are given the least. Did you check the teats on your does? A dairy doe (and buck) should only have 1 teat per side with each teat only having 1 orifice.