For those that dare, what you should do is pick a color shade and display a gradient of it across the screen from full black to full saturation of that color (using a decent graphics editing app). Does it look smooth or can you pick out "steps" in the gradiation? Are there areas where it almost looks grainy or "patterned" where it should just be a solid color? That's the indication of the "missing colors/bits". The problem doesn't really show up just by evaluating the overal color rendition of a picture on screen- as long as the display can hit the primary colors, you
will get a reasonable/satisfactory rendition of the image. It's the gradiation of colors (which are just another another way to express the many discrete colors referred to by that 16.x mil figure) that really isolates out the degree of color range. You can really entertain yourself and deliberately set your videocard to one of the lower color-bit settings (256 color, 16k color, etc.), and see what that does to the gradient.
(I guess that would constitute a test that leverages spatial AND color resolution at the same time...wink-wink)