No one color is likely to be "best", it depends on your requirements. Medium-light gray is the classic compromise for showing less dirt while still contributing some light reflectance. A "warm" gray will help balance the light qualities from a usually "cool" florescent lighting. Beiges and light tans would be warmer yet.
White floors are best for overall lighting evenness and finding dropped parts. They also make almost anything sitting on them look good, or at least do not distract from cabinetry and vehicles. Shows dirt more than the above colors.
Black is very dramatic and probably makes the widest range of vehicles look good, but is bad for working on them because they reflect so little light back up, and finding dropped parts is really bad. Shows dirt the worst, just like on a car.
The most common "color" for a floor seems to be a red oxide, maybe because for years past it was the most inexpensive because it used red lead. But any "color" is going to be more insistent, that is, you'll notice it more, for better or worse, and of course fewer other colors will look good with them. But the "right" colors will probably look even better than they would on a color-less (white/gray/black) floor. For example, a fairly bright "taxi-cab" yellow floor will really make a white or black car look good, along with red, black, or stainless tool chests/cabinets. A red Ferrari will look good on it (not that a Ferrari probably doesn't look pretty good just about anywhere) as would a lot of hot rods of many colors. But if you get tired of it, obviously it's a big time and/or money expense to change it.
, the pail is covering the wiring coming up from the floor for the 4 post lift that went inside the rectangle after these pictures were taken)
