Selecting and editing channels
You can select one or more channels in the Channels palette. The names of all selected, or active, channels are highlighted. Any editing changes you make apply to the active channels.
Selecting multiple channels A. Not visible or editable B. Visible but not selected for editing C. Selected for viewing and editing D. Selected for editing but not viewing
To select a channel:
Click the channel name. Shift-click to select (or deselect) multiple channels.
To edit a channel:
Use a painting or editing tool to paint in the image. Paint with white to add the selected channel's color at 100% intensity. Paint with a value of gray to add the channel's color at a lower intensity. Paint with black to fully remove the channel's color. (See Modifying alpha channels (Photoshop).)