I don't mean bleeding in the literal sense. I heard rumors that sousaphones "bleed" and leave marks on certain color clothing. Is this true? Well I kind of found it to be, a few months ago during the school year, we got some sousaphones fixed (this was during concert season though). So we unpacked them really quick and tested them out. Well after about 20 minutes of some goofing off, we decided to put the sousaphones back up. Upon doing so, we found we were covered in black residue on our arms and shirt.
What was this? The only thing I could even remotely connect it to is if some kind of residue was left over from polishing (we noticed they polished them up nicely!

). Is this common for sousaphones? I can't really think it is.
The reason I ask this is because we got night rehearsal tonight, and I was gonna just wear a white t-shirt (no dress code), but now I'm thinking otherwise.