The Tk demo directory has a file tcolor with commands for RGB conversion
to/from HSB. The file implements a simple HSB color chooser.
The conversion commands are duplicated in the BWidget SelectColor, which
uses them to draw a 2D hue/saturation plot on the canvas.
http://wiki.tcl.tk/54730
This is plotted as a square rather than in the form of the CIE color chart,
but it is equally useful for selecting colors.
Keith.