I had tried to get rid of a stain on my memory foam mattress a few months ago but it left a damp, yellow-outlined stain on the mattress. Following a google search, I used a foamy mixture of washing powder and water on the stain today, but my washing powder had blue crystals in it which left a large portion of my mattress with a blue-ish/purple tinted stain. It’s still damp. Any suggestions for what I can use to get the blue out?