My Lumia doesn't have the purple screen but my understanding is even if you do have it all you have to do is take the brightness off auto.
A very minor issue plus fix on the way doesn't equal (to me) a need to go to another phone.
I don't want to turn auto brightness off. Most of the time, the lowest brightness setting is the most appropriate setting, and that's when the purple screen issue occurs. Indoors, medium brightness is too bright and outdoors not bright enough. So auto-brightness is something that I'm going to continue to have enabled.
The purple screen looks terrible but it is what it is. I've come to terms with it even though it makes my Me Tile picture and my lockscreen background look terrible. It's certainly not a "minor issue," since the Metro design aesthetic is one of the things that drew me to WP7. Screwing it up, even with just one color, really damages the entire experience. Hopefully a patch will be released soon.