The Palette Editor Menu
The Palette Editor Menu can be accessed by right-clicking on the palette display in the Palette Editor, or by choosing the top entry from the dialog Tab menu. The operations in it can also be executed using the buttons at the bottom of the Palette Editor dialog.
"Edit Color" brings up a color editor that allows you to modify the color of the selected palette entry. If the palette is one that you are not allowed to edit (that is, one supplied by GIMP when it is installed), then the menu entry will be insensitive.
These commands each create a new palette entry, using either GIMP's current foreground color (as shown in the Color Area of the Toolbox), or the current background color.
"Delete Color" removes the selected color entry from the palette. If the palette is one that you are not allowed to edit, then the menu entry will be insensitive.