Making GIFs with ffmpeg: what does "transparency_color" do?
Solution 1:
The "transparent color" is the color that is mapped to transparent.
For example, if you have a web page with that image on it, and you use style sheets or absolute positioning or some other method to overlay the image on top of other items, everywhere in the gif that has that color, the items behind it (including the page's background) will show through instead of displaying that color.