hmm...you mean there supposed to be clean?
most of mine are tan or sand or grey and look sort "aged" - like me.
back when i was a working photographer i used to keep a lightly used (clean, non-scuffed, etc) bag or two in reserve for an assignment at the office or home or elsewhere for a client. the rest of the time i would launder or spot clean my personal non-working bags as needed.
now, i am less fastidious and don't mind a bag that has the odd scuff, smear, stain, etc. when the bag really starts looking bad i'll toss it into the washing machine on low with an old towel or two. i believe the towels help with the process by providing some gentle "abrasion" in the wash process.
breathe, relax and enjoy.