Yeah, it seems to be a common thing. Mine has a few pads that are a bit purplish and some that look a little greenish. Under each pad are LEDs in red, green, and blue colors. To get white, they turn on all three colors. As I understand it, the problem is that different LEDs can vary in brightness for the same electrical current passing through them. So if, say, the blue LED under one pad is a little brighter than the blue LEDs under the other pads, that pad will look slightly blueish compared to the others.
Obviously it doesn't affect the playability of the instrument, but it does detract from the aesthetics a bit. Kind of like a guitar with one machine head (tuning knob) a different color than the others. I'm hoping that Ableton may eventually be able to provide a software update that would let users "tune" the colors of each pad. If they can't, well, I'll just consider it one of the things that makes my Push uniquely mine.