Generally when you see pink or orange stains on the fixtures it means you have iron in the water. Well water needs to have a water softener or other filtering device to remove naturally occurring minerals from the water table from entering the piping system. Have your water tested to determine the exact mineral content. You can buy water test kits online or locally.
Another possibility is that bacteria called Serratia Marcescens is present in your bathroom, and possibly in your unchlorinated well water. It was once considered harmless, but now the bacteria is known to be an “opportunistic pathogen” that contributes to serious human infection. In particular, it infects people with compromised immune systems, most commonly with urinary tract and wound infections. Serratia Marcescens thrives in moist environments and can appear in sinks, toilet bowls, bathtubs, tile and other surfaces. It will not survive in chlorinated drinking water and the stains can be removed with chlorine bleach.