The color can be entered as a name ('blue'), hex or RGB code ('#0000FF' or 'RGB(0, 0, 255)'), or selected via the attached color palette in options.
When you specify the color that should change to the transparent color, then it matches this color everywhere in the GIF.
As a bonus, our app also allows making any GIF region transparent (not just the background). For example, if your GIF has a red background, then you can enter 'red' or hex code '#FF0000' in the transparent color field, and this red background will be assigned the transparent color index, which will make it disappear from the output GIF. This is a browser-based program that creates GIF animations with a transparent background.
