I don't mean this to sound glib, but I have occasionally had a problem when laundering a dark fabric, of detergent staying in the fabric and leaving just the sort of random lighter areas seen in your photo. You might try putting in the washer again without detergent and using cold water run it through the complete cycle again to see if that evens things out a bit. Just a thought.
Good luck to you.
Semper Fi,
Keith