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Heterozygous brown (Ata) is dark like this without DP. The dams are both homozygous brown, which is always lighter. It is due to the way the agouti genes work by restricting the black to the points. They do not add black to the points, they take it away from the body. Brown is the weakest of the 3 agouti genes. One brown allele only removes the black from the belly and muzzle, while 2 brown alleles have enough strength to push it back out of the body, while leaving the top line darker. The other agouti genes (A -- regular bay and A+ wild bay) remove a lot more of the black, and do not show any difference between heterozygous and homozygous.