Originally Posted by DCobb
I am far from being an expert in this area, but one way to steep the colors is to use the LAB mode in Photoshop and then use Apply Image with the a and b channels. Dan Margulis in his book Photopshop LAB Color fully discusses this. Interesting, you might give it a try.
You forgot to mention that Dan uses Apply Image on each channel in overlay mode.
A safer approach, also in LAB is to simply pull the high and low anchor points of the a and b channel curves toward the center. As long as you move each the same distance, your midpoint will remain at neutral and prevent a cast from creeping in, but the overall colors will not only be enhanced, they will be pulled farther apart from each other, something that RGB can't do as effectively.