It looks like you are trying to edit one of the library palettes, but they are probably read-only.
Can you try saving the palette under a new name (the save palette as icon in the top right corner). You should then be able to edit the new palette.
May b u r right dear.. but this only occurs in X6, before this i was use X3,X2 they can save any new colour as i doing now..but i think there is error in X6. i m not saving colour plate i m just adding new colour in the plate and how this possible? within default plate which always present.