There's a lot of different ways of doing it. Sometimes I'll manually select each color in a ramp, but more often I do something like this-



I manually selected the yellow and the blue by typing in the RGB values for them. That blue is actually one of my favorites, RGB-(128, 128, 255). I colored the left square yellow and all the rest of it blue. I then changed my brush opacity to 75% with the yellow active and colored over the 2nd from the left square. I then went to 50% for the middle one and 25% for the 4th square. It's now an even blend, or close enough.

I would then use this palette to make whatever pixel art I'm making. At the end I might decide to manually adjust some of the colors. Take my current avatar for example. I don't think there's a single color on it that I didn't manually adjust at the end. Sometimes these adjustments take the form of selecting all pixels with a certain color, making a new layer, and filling that layer with a new color. Then I'll adjust the layer opacity so it mixes that new color with whatever was there before, until I find a good balance.

There's a ton of other ways of doing all of this though.


Also, the HSB color model is great in some ways but a little messed up in others. Really, saturation shouldn't affect value, but in HSB it does. Here's something I made not long ago-



Notice that jagged line going from left to right? That shouldn't be there. In HSB it is, because of how color is calculated. Above that line value, "B", is 100% and saturation decreases as you go up. Below that line saturation is a near constant 99% and value decreases as you go down. Now it's not impossible that I didn't make it exactly right, so I'll check it later to make sure. I don't have time for it right now though. Actually I'm fairly sure that it's not completely perfect. I'll try to get a better version made later.

Edited by tanuki - 24 April 2011 at 4:54pm

Recently I was playing with adobe illustrator's "blend" feature that makes blended averages between two things by a chosen number of steps. Here's one of the palettes I made-




All of the named colors, the middle one and the ones at the ends of each branch, were chosen from this list of colors.

I liked this because with 6 main colors I could make 10 ramps that were all related.

tanuki: If you used a program that works in indexed colors, it would be much more user-friendly, with Palette changes applied on the image in real-time.

It sounds like your ideas about what indexed colour is are a bit vague. I suggest investigating the wikipedia 'indexed color' article.

I'm also getting the impression that you have the idea that it's possible to invade other people's software with your code and alter the behaviour. If that is the case:
generally, that is not the situation. Although if you were using GIMP, it would be pretty straightforward to make a plugin which does the adjustments you want

..
as for associating different color indices, you could do that by laying out your palette in a specific way.
Like this, for example: the first 8 colors for one group
(this could include unused slots, which would be black),
the second 8 colors for the next group, and so on.
Then your program would just adjust the L,A,B values of the whole set of 8 at once.

You could (the limit of what you can program is exactly 'any deterministic process', which resolves to 'any process at all' -- Turing and others provided scientific proof of this.
With the further constraint 'anything you can actually conceptualize in full'). I suspect you don't mean 'arbitrary' as an arbitrary color wouldn't be a visual cue at all. I suspect you want to calculate a representative color based off of the colors in the set, and then normalize your color values relative to that before performing any color adjustment.

Your ability to actually code that is primarily dependent on your own ability to conceptualize it in detail.

Neat. How'd you manage that?

And neota, yes, I did mean representative.

I think a straight line, but in LAB colorspace, is better
(just easier to think about, and more consistent/uniformly nice looking)
Implementing LAB support is possible but non-trivial in Lua
(the non-trivial part being matrix application)

Oh, that's what you meant. I confess I've only tried splines for larger gradients, like say 16 slots with 5 colors filled in + cubic splines (I think you are doing conic splines here). It works great there, although, I was never able to overcome the issues near the edges of the curve to my satisfaction.
Eventually I concluded that, with a linear LAB gradient as a base, it was just easier to tweak the colors.

So from my PoV, how useful this is gonna be depends on how easy it is to use.  It has to be REALLY EASY to beat the simplicity of plain gradient+tweak, especially for works with a small palette.