I had this idea a while back for a way to represent an HDR color swatch. The concept should be fairly self-explanatory based on the below movie. Basically, a soft-edged black vignette is multiplied with the user's selected color in linear floating-point color space. As you can see, this makes it easy to see what color you've selected, even when that color is “unseeable,” i.e. whiter than white. How “crushed” the vignette becomes gives an intuitive sense of how overbright the color is.
An RGB picker is shown here for simplicity, but obviously this would work with any color selection model.
Created in Adobe After Effects 6.5, using eLin.
by Stu Maschwitz