I think that's part of the reason. If you wear all black, people remember your silhouette, not the individual pieces, I think. Alt has said that she wishes she could wear the same outfit all the time, so she doesn't seem to feel a need to experiment much with color. And if you are tall you can make a very striking silhouette with black. I can imagine she feels a lot of pressure to look the part, so going black is safe. And of course, when everything match, you have more time to think about other things. I imagine this is true for a lot of creative minds.