This colour- visualization we may do every time we banish certain habits and thoughts, that are contrary to the following Forces of the Heavenly Father and Mother Earth (1, 2 and 3 going backwards, and 4, 5 and 6 going forward again): 

 The Colours also correspond with the different "layers" or "bodies" of the aura. So you can also imagine you are, starting at the physical body (red), cleaning up all of your aura from the inside out:

• Material Body: visualize Red
• Astral Body: visualize Orange
• Mental Body: visualize Yellow
• Causal Body: visualize Green
• Buddhic Body: visualize Blue
• Athmic Body: visualize Dark blue

  Sometimes the following will be of help for learning to be able to visualize the colours: look at the breaking of sunlight by a prism-crystal,  

or (if you don't have one) for some time watch the separate colours of a picture like below. Then later on try to visualize those colours, also without this picture (with closed eyes for instance). Just try the picture down here: