Using the button above the histogram you can select the channel to be edited. You can switch between selecting the RGB (complete) channel or individual channels (colour layers). Independent settings can be made for each channel which will then be applied in the image (see below).
Warning: It is not possible to apply both the complete and the individual channels simultaneously! The reason for this is the fact that changes in the RGB (complete) channel affect the individual histograms and vice versa. Consequently, the settings of the respective channels would then not match the settings in the original histogram. For this reason, when exiting the dialog box a query appears asking you whether you want to use the RGB (complete) or individual channels.
