Set the way locked colors are handled when your palette is (re)generated:

1. Append colors

With this option, any locked colors will be appended on top of the generated palette.

The resulting palette will often contain more colors than the number set in the Colors option.

2. Replaced with nearest colors

With this option, any locked colors will replace the colors closest to them in rgb value, in the generated palette.

3. Replace with least used colors

With this option, any locked colors will replace the colors with least coverage in the image, in the generate palette.

With both option 2. and 3., the resulting palette will always contain the same number of colors as set in the Colors option.