In 24bpp mode - palette IS NOT EXISTS (because all 16 million colors available for using). And in 24bpp mode in palette window - UNI-palette color grid showing only for convenience of color selection. Also in 24bpp mode you can use 'Spectral select'. And 'edit' command (in palette window) in 24bpp mode changes directly FC and BC rgb-components values. When you enter in palette in 24bpp mode - then in 'Spectral select' and 'Palette grid' colors will be reseted to FC=black and BC=white. Bacause of it - if you change current FC and BC in 24bpp mode - press double 'right soft' in painting window for showing Edit-mode of FC and BC (first click in painting window will show palette grid, second click already in palette grid will show edit-mode)