The following image shows a scene in their channels - the Actions assume your picture is in landscape orientation and shrinks them to 400x300 pixels, so not to use up too much memory.
The first line is to introduce you to Lab (in colour!), the next two lines are the results of running the two Actions.
| Full image | Lab 'a' channel - in 'a' colour | Lab 'b' channel - in 'b' colour |
| Lab Luminosity channel | Lab 'a' channel - gray scale | Lab 'b' channel - gray scale |
| RGB Red channel - gray scale | RGB Green channel - gray scale | RGB Blue channel - gray scale |
Notice the red barn and blue sky in each channel - and it is not more obvious that green grass is a mixture of -ve 'a' (green) and +ve 'b' (yellow) and than in the RGB channels? This is why I find it easier to change colour in Lab rather than RGB.