Converting your images into Lab mode can have several advantages when adjusting or retouching your images. One of these advantages is the way lab mode allows you to saturate your images while driving opposing colors apart. Lab mode is a very powerful editing mode but also a dangerous one as you can easily introduce unprintable colors and colors outside your monitors gamut. In the Lab colorspace many of the color adjustment tools work in a completely different way to those in the RGB colorspace. The red, green and blue channels are replaced by the Lightness and the a (green as opposed to magenta) and b (blue as oppose to yellow) channels. This method is relatively safe if used in moderation, you do not have to delve deeper into the complexities of the Lab mode.
- Under the Edit menu convert your image into the Lab mode.
- Create a curves adjustment layer. make sure your the grid has more detailed lines in it by alt/option clicking on the grid.
- Select the a channel and move the top of the curve point to the left by either one or two grid spaces, move the bottom of curve to the right by the same amount.
- Repeat this procedure for the b channel.
- Reduce the opacity of the adjustment layer to reduce the effect.
- Flatten the image and convert back to the RGB colorspace.
It is very important that you convert your image back to the RGB colorspace before printing or sending out to the client. You could also record the above as an action, but beware out of gamut colors (Shift+Apple+Y).