A stain on clothing is read as worry about a mark on your reputation or a mistake you fear others will notice. The dream often reflects self-consciousness more than any real fault.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.