Is painted vs has been painted

I think you are confused because we have two different uses of 'painted' here. There is the verb which describes the process of painting something, even if the action is in the past (I had a decorator come yesterday and he painted my door brown) and the adjectival usage where we use 'painted' to describe the condition of the door after the action of painting it has been completed (You can tell which is my house becasue it's the one where the door is painted brown).

This use of the same word both a verb and as an adjective is actually quite common. In terms of doors we can also do it with the word 'lock' ("The door is locked when we leave" as opposed to "I can't get in because the door is locked")

We can also do it with food ("I sliced the bread so that it was ready for toasting" and "I want a loaf of sliced bread, please.")