Adobe Illustrator - Lock Important Colors In GIFS When Using Save For Web In Illustrator (9/10.x)
When you're saving a graphic as a GIF, the GIF algorithm chooses the 256 most represented colors in order to create the palette. However, you may want to save your GIF with even fewer colors than 256, and this can cause an important color to be dropped from the palette. To prevent this from happening, in the Save For Web dialog box either select the color and click the Lock button or choose Lock/Unlock Selected Colors from the Color Table palette's pop-up menu. A white square with a dot center appears in the lower-right corner of a locked color. By locking important colors, you prevent them from being dropped or dithered when you reduce the number of colors in the image. You can unlock colors by choosing Unlock All Colors from the Color Table palette's pop-up menu.