Since version 0.87, the editor includes functionality that lets you more easily customize a civ's palette. You can access this functionality by going to the CIV tab and then clicking the "Edit Civ Colors" button.
You'll then arrive at the Color Palette Editor screen. To understand how this works, it will be helpful to have some understanding of how Civ colors work.
We tend to think of a civ having two colors - the default, and the unique. The Iroquois get purple, the Zulu get either yellow or black, the Chinese get either lavendar or teal, etc. You can switch it up, but each civ has two colors.
However, it's actually more complicated than that. Each civ color corresponds to a PCX file. That PCX file only has a single pixel, but it has a palette with 256 colors, just like any other Civ palette. And 70 of those 256 colors in the palette are used in various ways by Civ III. Most of these tend to be similar enough that this is often overlooked, but there often are subtle differences between the civ color in the editor, in the histograph, in the diplomacy screen, and so forth.
Some enterprising individuals have experimented with creating new civ colors, and even creating hybrid civ colors, where two or more colors are combined in a single PCX palette, created dual-tone or even shimmering units. Rhye wrote a guide on this that has been used as a reference when creating this component of the editor; the goal of this window is to make it easier to modify civ colors (including experimenting with dual-tone units), and expand civ color customization to a wider audience.
There are four basic functionalities on this page, which will be explained in more detail later:
The first thing you should note is that, as this does modify the ntp**.pcx files, you'll want to have BIQ-specific versions of these files. In fact, to protect your original files from accidental overwriting, this portion of the editor isn't enabled in the editor if you don't have custom ntp**.pcx files somewhere in the BIQ's scenario search folders.
Changing the color you have selected in the Select Color dropdown will both switch colors, and save the previous color. Exiting the color palette editor will also save the most recently edited color. If you have a color that you like and are tweaking it, it's advisable to save a backup copy of it before continuing to edit it.
The check boxes along the top let you choose which colors are currently visible. "Rhye's Recommendations" are a set of colors that Rhye recommends modifying to create dual-tone units. "Shades of main colors" is just what it says - the 16 main colors. "Other useful colors" are the last 6, which also feature prominently. "All Others" are also shades of the main color, but tend to be noticeably more different than the first few groups. "Shades of Gray" is what it says it is, and is generally very similar between civ colors - changing these isn't really recommended. Likewise, the "Shouldn't Change" colors are very similar between civ colors, and changing them is at your own experimentation.
Functionality 3, changing a specific color, is accomplished by clicking on the color. This brings up a color chooser, which will give you several ways in which to change the color. The specifics depend on the version of Java you have - newer versions of Java have fancier Color Choosers. I'll explain the options available in the minimum required version of Java, 1.5, here:
After using one or more of these options to choose your palette color, click OK, and the palette color will be updated.
The final functionality, adjusting the hue, saturation, or balance, of many palette colors at once, is the quickest and most powerful. Clicking it will bring up a window where you can use a slider to adjust the hue of all the civ-specific colors (specifically, all except "Shades of Gray" and "Shouldn't Change") at once. Simply drag the slider, and the "Color" bar will show you what the first color will look like. Click Accept when you are happy, and all the colors' hue will be adjusted by the same amount that the first color was adjusted. This is, for example, a very quick way to change from a blue-centric palette to an orange-centric palette.
As a word of warning, adjusting the balance tends to result in the colors become more similar. Adjusting the saturation tends to be more forgiving, although if you set it very low some colors may turn red, and if this happens you'll need to bump the hue settings to get everything back in sync. Adjusting the hue is generally the most forgiving. If you find a color you like, it's a good idea to back it up prior to further modifications.
You'll need to reload the editor to see the changes in other areas of the editor, but they are saved to the .pcx files as soon as you leave the Color Palette Editor.