ABS plastic swell and print quality differences

      Something has been bothering me for a while. At first I thought it was all in my head, then I ran a few tests. Basically, I've been noticing differences in the print quality and characteristics of different color plastics. When I first got my 3d printer, I stuck with mostly blue and green, with the occasional red ABS filaments. I print primarily 3mm ABS, with the occasional PLA print. I've tried at least 8 or 9 different colors, and from what i can tell, each color has a different "swell" factor while extruding. Green, Blue, and Natural have minimal swell, while White ABS has a horrible swell. I've taken the time to measure the input filament diameter (in most cases it's around 2.9xxx mm). 

      White is the worst offender. Shown below is a simple knob printed on my Makerbot T.O.M.. In each case, identical print parameters and speeds were used. As shown, the Natural color ABS plastic looks almost perfect, while the White ABS looks horribly overfilled. Because the input filament diameter was identical (2.92 mm) and the identical GCode file was used, the only logical conclusion that I can reach is that the White ABS must somehow be expanding more than the Natural color during printing. I'm wondering if the dye or pigment used is causing this somehow.

      Out of all filaments that I've used, the Natural ABS plastic has the best printing characteristics. Red and Green are a close second, Red's not bad, White is a monstrosity. Anyone else have issue such as this?

Identical prints?