Liner in proofing basket has red streaks

I noticed the same thing, a couple of times, when I used canvas as a cloche but I think the streaks, there, were blue. These are a reddish brown like someone put them there with a pencil and, when I pulled the liner from the dough, the streak was on the dough. I assumed they were some kind of mold so I washed them by hand. This is from proofing sourdough bread overnight. The cloche ones were on the counter but these reddish ones were in the fridge (from separate times long ago).

My canvas cloche, they came clean, but these two reddish lines are still there. Has anyone seen these themselves and know what they are or where they could be coming from?