I have a custom rifle on a 98 Mauser. The barrel Douglas and was their latest new steel in the day, middle 60s. The gunsmith who made it up was known for his bluing. When he blued this rifle the action was perfect and still is. The barrel came out pleasingly PLUM. He wanted to reblue but we just left it that way, it has character.
I have old Ruger Single-6 that has a wisp or two of purple on the frame. I have never herd WD causes purple. I think whoever started that one is full of brown.