Black etches brass cases quite strongly. I don't worry about the discoloration. I deprime, run them through 3-4 hot, soapy water rinses, let them dry then resize, most of the time only neck size, then run them in my tumbler about 3 hours. I go through more media than when I loaded a lot of smokeless but it's well worth it to me.
Probably 25 years ago I bought a 12 hour timer, a handy box and put a male and female cord on it. I plug my tumbler into the timer cord, plug the timer in and set it for 3-4 hours....works great.
