To be clear, since the dam is self-colored black, she had to give one copy to each twin, so they are heterozygous for the self-colored agouti gene. The twin ram lambs are not only dark, but like their sire they have a very strong load of the reddish-brown pheomelanin pigment. These are going to be quite nice looking rams. You may note that the ram on the left also has white spotting exhibited. Although you can't see it in this photo, the sire Fedan has a white poll spot and a white spot on the side of his neck. But for the ram lamb to exhibit white, he has to be homozygous, thus had to get a copy from his dam Bonita. I had no clue from Bonita's prior 4 lambs (all of whom I own) that she carried white spotting. You may note that Fedan was a ram I included in my Picasa album as a suspect for carrying self-colored black, so I halfway expected black lambs from his breeding with Bonita. (This outcome of course does not prove he doesn't carry black.)
My conviction about the phenotype of very dark mouflon Soay sheep being heterozygous for self-colored is growing stronger.