+1 (for sebas' comment, not for the rainbow folders) I don't mind the idea of being able to customize folder colours, but I don't think that it should be done like this - we do not have the 'folder colour' settings in the colour scheme settings, which means that some other colour will be used to do this (bad idea!).
We have had more than a few problems in plasma theming that came from "we can use this element for something completely irrelevant, because it looks pretty with the default theme". Cheers, Ivan p.s. The message with the screenshot of what it looks like for me is waiting for moderator approval.