I can say that I too have seen this purple thing happening to the undersides of 2 different toilet seats (both are wooden... one is white and the other is light grey). The only thing I have found to remove it is an abrasive cleaner like comet or ajax probably because of the bleach in them. BUT you can't use those on the top. I originally tried removing it with a lysol wipe thinking it was possibly dried blood and when that didn't work at all I was truly puzzled.
I know I have seen this discussion before on here about Pentasa. I wish they would say something about this in their literature because I KNOW it is doing this. I have ruled everything else out.
Crohn's, Migraines, Fibromyalgia, Hypothyroid, Polychondritis, Pericarditis, Anemia, Depression, PTSD
Lacto-Vegetarian Low Residue Diet
Solgar V-75, Gentle Iron, Calcium, Vit D, Flaxseed Oil, B2, Biotin, B12 shot, Turmeric
Pentasa, Metaprolol, Gabapentin, Synthroid, Omeprazole, Flexerol, Zocor, Xanax, Fiorinal
Was on Entocort, INH, Prednisone, Prednisolone, Cipro, Flagyl
1st surgery in May