Hi Ralph,


To [hopefully] answer your questions.


The white one is used when you just take a "normal" photo using your 580. It will soften the harshness of the flash especially if you use it correctly [ not familiar with sto fen I use gary fong lightsphere].


The yellow you use when indoors and shooting in place lit with incandescent bulbs, just remember to set you white balance to incandescent bulb. It should give you a more natural looking / "ambient light" effect rather than when you shoot with just a white a white diffuser or bare flash whereby you will tend to see you become become bluish and the background in somewhat orange color which is not really nice.


Blue ones are usually used to give a cooler look to a picture. I remember I used to use an 80a color correction filter when I was still shooting film. I use this when I myself taking the picture of a subject illuminated by those video lights that give off a somewhat orange light. But now in the digital age I haven't really tried shooting with a blue diffuser.


By the way CTO means Color Temperature Orange at least thats what I remember it to mean. heheh[]


Hope this helps