Color differences these days will be due to the color settings and monitor. All color information is sent digitally over HDMI/DVI Link/Displayport. AMD did have better color back in the analog VGA days because they had a better 2D processor, but any perceived color differences now will be due to the initial color setting or monitor used. Or the age old placebo affect.
First thing I do when I get a new card or monitor is calibrate the card first to make sure its sending out a base signal, calibrate the monitor accordingly, then recalibrate the card again to my tastes (which is generally a neutral output (not warm or cool) with a slightly higher contrast/color vibrance from base (really takes advantage of LG's superior color display over PC IPS). Then enjoy that setup for years to come without touching it again.