The rMBPs I've run (including my own) across have had very uniform brightness and white color. I'm curious which manufacturer made the LCD in yours because--going from the usual problems with Apple LCDs.
If you aren't aware, you can tease out the LCD manufacturer via the model string and this command:
ioreg -lw0 | grep "EDID" | sed "/[^<]*</s///" | xxd -p -r
If it begins with LSN, it's a Samsung (which tend to be the good ones); if it's LP, it's an LG (which, unsurprisingly, tend to be the poor ones).