What is the pink color on my shower walls, corners and grout?

That pink color that is often found in showers with high use or no ventillation is called Serratia Marcescens,it is a bacteria that feeds on soaps and shampoos.Serratia Marcescens can build up within days of cleaning your shower. The only way to get rid of it is to bleach your shower weekly and wipe down the walls after cleaning.