public void setTransparent(Color c) {
        transparent = c;
    }
Sets the transparent color for the last added frame
and any subsequent frames.
Since all colors are subject to modification
in the quantization process, the color in the final
palette for each frame closest to the given color
becomes the transparent color for that frame.
May be set to null to indicate no transparent color.

@param c Color to be treated as transparent on display.
plugins/base-plugin/src/main/java/com/github/hui/quick/plugin/base/gif/GifEncoder.java