See that arrow way over to the right opposite the word 'Layers' in the Layers panel? Click on it,
click 'Add Tab' and a host of options are displayed. Try 'Channels' (it will open as a tab in what
is now labeled the 'Layers, Channels' panel. Channels will allow you to edit the individual Red,
Green or Blue channels of the full color image. Click on a color name, then click on the 'Colors'
just above the image. Have fun.