I love LAB colour. It is one of the best color spaces for a variety of reasons. You may not be aware of this but sharpening works best when it is applied to the luminosity of your image only. Normally sharpening in Photoshop will change your color values slightly as well as your luminosity.
The solution of course is if you are in RGB is to sharpen on a Luminosity layer. The other approach is to do it in LAB color because LAB separates the Luminosity. This great tutorial by Harold Davis explains how to use sharpening in LAB to add some depth to your image.