A lot of Lumia 930's and Icon's have bad quality AMOLED panels. Mine had a really bad one too with purple spots all over. I replaced the screen and the new one is almost perfect, the only problem is when on a white page the bottom part is white and the top part is a tad purple but not with big spots as the previous one. For now i'm satisfied since most is dark in the UI. Probably i'm replacing my screen in a while again when a new batch of screens arrives.
(working for a phone repair/service shop)