I've been storing my starter in a jar with a metal lid, and finally learned my lesson. I neglected the starter for 3 weeks, and when I went to feed it, it had little rust spots on top of it. Would you toss the whole thing and start over, or would it be safe to scrape off the rusty parts?
if it is just rust, try and use some from the bottom of the jar. Get that back on its feeding schedule and it should be fine.
Or red mold? How do you know it's rust?
There is red rust on the metal lid, so it looks like it just dripped down onto the starter.
no problems then. Scoop it out and keep going with what you have left. It'll be ok