Pictures Right, Examples of the green being added, boosted and removed with the Add Colour, Colour Boost, RGB Remover filters (original image top left).

Pictures Left. Top, This cars red paintwork has been brightened using Colour Boost, leaving the rest of the image untouched.
Middle. Using Add Colour to place just yellow on the cabs in this greyscale picture.
Bottom. Here the sky has been replaced by first, removing it on the alpha channel with the RGB Remover filter.

Main Page Pictures. Top Left, Both red and blue added to this mono image using Add Colour.
Top Right. Using two layers, the red bodywork has been removed from the top layer using the RGB Remover filter. Now a whole range of effects can be applied to the lower layer, showing through on just the cars bodywork, replacing the red.
Bottom Right. The yellow and the magenta have both been enhanced with the rest of the image unchanged.