The GTK Color Selector

The GTK Color Selector is similar to GIMP's standard color selector. The main difference is that you can't select in which color space you want to work. The left color bar is always working in value mode and you can alter the hue and saturation by dragging your mouse in the circle.

Another difference is that the RGB values are represented in percent instead of values from 0 to 255. 100% (1.0) is 255 and 0% (0.0) is 0. The fact is that you should see it as the amount of e.g. red that you want to mix into your color.