[css-color] copying a value from another color

It would be very useful if color adjusters could take a color parameter,
instead of just a number or percentage, and simply take the color's value.

For example, trying to express a color with proper contrast from a
background color, and using the hue of known color:

color(var(--background) contrast(0%) hue(var(--color-theme)))

side note: contrast(100%) is always either black or white, and I would
guess would be used a lot less than contrast(0%) which finds the minimum
contrasting color. It's odd in my mind that the default if omitted is 100%.