Hey,
Today I wanted to play normal minecraft and when I logged in I had black stripes on my skin. I've tried to set my skin to slim on the minecraft website but that didnt work. I tried it directly via a skinsite, didn't work either. And lastly I tried to change it in the launcher itself and that didnt work as well (even though it still showed slim in the launchers preview). Even when I selected the Alex skin in the launcher, when I launched the game it still showed the black stripes even with a preset slim alex skin. The skin that I used has worked for almost 2 years.

Is it possible that it happened because I downloaded MultiMC to play modded 1.10.2?