the Pixel Depth is the Number of colors
32bit = Trillions of colors. The Colors are Derived from the 3 main colors, Red Green Blue
Red Green and Blue can be a number from 1 thru 255
say, 255, 0, 0 would be Red!
RGB can also be Translated into HSL
which is Hue Saturation and Lumanence[sic]
and it can be translated Vice Versa, and are even sometimes used together to be sure of the right color(as in models when lights are around it).
Well, thats my in depth view at Pixel Depth... just dont ask What is Color, that is the hardest thing to explain good! heh heh