It looks like you can insert 2 drives into the upgrade thing. The first drive was level 1 i think, and i accidentally inserted a second drive into the machine, which made it look like there is only one drive, but with yellow color(usually blue). Its not anything critical, as i can just remove them both from the machine (even though a little bit buggy), but wanted to note this out!
Viewing post in Voices of the Void 0.8.2 Bug Reports
This can happen due to an old bug when this exact slot can't decide whether it has a drive in it or not (you might have noticed how you can't save a signal on an inserted drive after processing). Also, drives with a copy of a signals have these yellow lights (you can make a copy by saving a signal on a computer). Not sure why this happens, but it's harmless