Filters can make GIFs smaller
A grayscale GIF needs only shades of grey, so each frame’s 256-colour palette goes much further — gradients look smoother and files often shrink. Faded and Noir looks reduce colour variety too. Vivid and Warm push colours apart, which can increase banding on photographic content; pair them with moderate sizes.
All filters are applied as a colour matrix to each pixel, which keeps the effect identical on every frame — no flicker between frames.
More creative effects
For animated colour changes, try Rainbow GIF. To hide or soften part of the image, use Blur GIF. To replace a background, use the GIF background remover, and to label the result, add text.