Have been planning to write this script for a while now but never got around to it. Its strength lies within its customizability. If you want a specific color to occupy a larger span of space in the spectrum then simply list that color twice (or multiple times):
spectrumbar red, green, green, blue
This will produce a bar where the green section occupies more of the bar. Further customization can be done by automatically defining a rainbow spectrum but this requires borrowing code from Robert Cambell's script(s) (namely the hsv to rgb conversion).
Also, the length, head, and tail options need to be cleaned up but, realistically, it isn't necessary to touch those options.
Sean 01:55, 3 Sept 2009 (EST)
Just added rounded ends for aesthetic look
Sean 08:25, 9 Sept 2009 (EST)
Made some changes to the way the colours were being recognized as it couldn't handle colour specifications like "gray10" where there's a mix of numbers and letters (before it reserved numbers to R,G,B values and letters to PyMOL color values). Now it checks the command line input. If it sees that the input contains both numbers and letters then it will check to see if it is part of the list of colour values, if not, it will return an error. This should be fully functional now and was corrected as requested by a user from the PyMOL mailing list.
Sean 13:35, 6 Nov 2009 (EST)