Relative colors in CSS?

Hi.

Do existing CSS standards, or ones being planned, include a way to define colors relatively to their parents? 

Example:

BODY {color : #CCCC99}

P {color : darker}

The reason I'm looking for this sort of solution is that quite often when designing pages I use a set of colors that are more or less variations of the same basic color. The background is a light tone, the following layer (div) a bit darker, the following even darker plus a bit more red, etc. 

Since almost all other values in CSS can be either absolute or relative (to their parent), it seems only natural that colors would also. 

A suggestion for different values: 
Brighter, decreases all RGB values by, say 5%. 
Darker, increases all RGB values by 5%. 
+red, increase Red value by 5%. 
-red, decrease Red value by 5%
++ by 10%. 
+++ by 15%... 
and combinations (or shorthand) +red --green +++blue

Having a way to define relative colors would IMO improve scalability (the author would only have to define one starting colour, that could easily be replaced by User stylesheets) and thus increase overall flexibility.

Regards, Miki Wiik