I used to colour my hair then I noticed I was starting to loose my hair colour around 60 I let the colour grow out and my “natural” colour was white. I never coloured my hair again. I use a purple shampoo and am very happy with my pure white hair.
I have only used body wash for some years now and have not had a problem with soap scum even though I use shampoo to wash my hair. I also wash down the tiles after every shower. I have a small hand held shower head for that purpose.