The GIF specification only allows for images with a maximum color depth of 8bit, which is 256 unique colors. Cyotek Gif Animator allows you to add images to an animation with greater than this number of colors, but such images will be automatically processed to use 8bit colors using an octree quantizer when saving the animation. To avoid this automatic adjustment, either only add images that are 256 colors or less, or use the built in tools to manually optimize images prior to saving the animation. The animation reel indicates the presence of non-optimal images by displaying the icon in the upper right corner of the frame preview. Each frame in the animation can either use a local or a global palette. The advantages of the global palette are that generally you would expect to see a smaller file size and are useful if all or most of the frames in the animation share the same set of colors, or the sum of all unique colors in the animation is 256 or less. The advantages of using local palettes is that each frame can use it's own set of unique colors, at the expense of a slightly larger file size. However, you don't have to use one or the other, you can have some frames using a global palette and others using a local palette as appropriate.
Gif Animator provides the ability to optimize images to other the local palette or global palette, and to generate a global palette based on frames in the animation.
If Gif Animator has flagged an image as being non-optimal, you can either let image being auto-optimized when saving the animation, or you can optimize it yourself. Doing it yourself gives you more control over the process.
To optimize an image: