The stock Virtools BBs have no means to get and set color components through their hue/saturation/value representations. Some BBs are aware of HSV, such as Interpolator BB, and the Rainbow Color paramop apparently takes hue and value as its inputs.
Here are two VSL blocks to convert an RGB representation of color to HSV and vice versa. Example of this in action here.
http://devlab.flashbangstudios.biz/article.php?story=20050718154418636