murals

Hi all. I did this mural on a North facing exterior wall that does not ever get direct sunlight. Something has caused the smoothed-out colors (on the right) to "bleach" in spots, resulting in the current state (pictured on the left). They swear they have not treated the wall or powerwashed...

Wondering if anyone has any expertise or experience with painting or attaching large vinyl murals or graphics on water towers? What works best and how much does this type of service cost?