Kelly Kissane, a colleague at WOU, brought her biology class on a spider-hunting trip to our ranch last week. My theory is that they used the spiders as an excuse to pet the alpacas (as if you need an excuse!)
I sent Kelly the link to Consuella's baby here on the blog, and she sent me this email to help me understand why brown + white = black.
She agreed to let me post her response here. Enjoy!
I teach genetics, and do behavioral genetics research. I have a guess as to the genetics of the little guy so far, which matches genetics in other animals (horses and cattle are a bit different), based on the information you gave:
Dominant non-albino white is epistatic to all other colors (same in cats).
W- is white, ww = non-white B- = black, bb = brown
Sire (white) = Ww Bb
Dam (brown) ww bb
newborn(black) - wwBb
If I'm right, then 1/2 of the time you will get white, 1/4 will be black, 1/4 will be brown with this cross.