Do you think of a white flag as a flag of surrender? It would be more accurate to describe it as a flag of truce. In military terms it is an appeal for a ceasefire to meet for a parley. The corresponding passage in my word is come and let us reason together.
Your sins are an issue that must be resolved between us. I invite you to come, and let your flag of truce be a flag of surrender, for you must surrender to me. Yet if you confess your sins I am faithful and just to forgive you and cleanse you from all unrighteousness. Then your sins that were as scarlet will be as white as wool.