Color of DVD and Blu-ray Disc

[ranma]

When I first watched blu-ray disc, I was not only impressed by the resolution that blu-ray provided, but also the depth of the color. I checked several online technical articles, neither of them mentions the color space of DVD and blu-ray, as well as the blu-ray advertises. So I begin to wonder, is there difference of color depth in specs of BD and DVD, or it is just the higher bitrate and storage space that allow studios to get more colors into the transfer instead of heavily compress them?