I have one...it's sort of oriented to ease the addition of stuff like tattoos or different fur patterns (like tigerstripes) camouflage on sprites.
You all know how when you are making a sprite you usually make a choice at one point in time when you say, "i'll have 3 tones per ramp for this one" and then you proceed to shade everything and interrupt your shading every time you are going to color a different section of the sprite (for example you are done shading the blue parts and you're starting the red ones) this makes it very hard to add any sort of complicated patterns over the skin/fabrics of the character.
The idea is that the depth itself, the lightness is handled in a single ramp. that way you make a single value/lightness pass.
Knowing that you've got the depth all taken care of, you proceed to create the equivalents of your original ramp in different hues. Say if you had 3 red colors originally, and you need to have gray and blue hues as well, you make 2 new ramps of 3 shades each, making sure the shades have similar lightness to your red ones.
This would make it much much easier to make characters with several different print patterns on their clothing, or if you mess up in the middle of putting the pattern on you dont have to re-trace your steps in undo, you simply change the hue information on it and nothing is lost.
This would all be handled internally, nothing would change in the end product, only in the inner process of coloring the sprites. You could even tell the program to for example use the same shade for the darkest red and blue shades for example, but if it turns out for whatever reason you can use more shades than you originally thought, you still have the separation of the two shades in the hue information, you just need to tell now instead of using that gnarly purple for your darkest blue and red hues, you'll have actual dark red and dark blue.
The people in SF3 obviously used this kind of tool, only to a much greater degree
http://www.zweifuss.com/colorswap.php?pcolorstring=IbukiPalette.bin&pcolornum=0&pname=ibuki/ibuki-jump.gif most evident in this particular animation. Oddly enough, even though they developed the tool they didnt take incredible advantage of it...as most people dont even notice it. obviously, it helped in making the Gill character posible since it would make it a simple matter of changing his hue information.
SF3 uses it in an even greater degree than I described, because if you pay attention closely...they do not only have different hue information for every part of the sprite, they have two totally different and separate palletes that go from the brightest color to the darkest color for every single frame. That is how they make their two lightsources, they have the normal sprite and the blue sprite, then they use some kind of tool to tell the painting program which part uses the blue hue, and which one uses the normal white hue.
if you think this could be of any use at all...I have an even more complicated idea about this...involving actually completely diferent shadings for each hue.....it would be useful for characters that have chromed armor and normal clothing...