Re: rainbow staines
It’s known as iridescence on glass and is usually caused by;
Detergents with high levels of disilicate
Very soft water
Long cycles at high temperature
It is permanent damage and cannot be reversed. 🙁
On your stainless I’d take a guess and say that it was poor quality stainless as it happens on that or it could be a chemical reaction to something on it, the detergent/s or softener used or simply touching another item that is causing a reaction.
Hope that helps
K.