eth:Shoot in RAW mode. Why shoot a gray card for every lighting situation?
So the color is correct straight out of the camera. I like to show my clients the raw images, directly after shooting, and I want the color to be perfect.
This is the reason why cameras have a custom white balance setting, so you can get good color straight out of the camera.
After setting my custom white balance I also make an exposure with the gray card in frame, using the new custom white balance. This is so I can check my color and adjust if needed. Having a reference shot eliminates the guesswork. If the color is on I know it, if it's off I know exactly how far and which direction and it's a one click fix.
If perfect color SOOC is not important to you then by all means, continue to let your camera guess and spend your time fixing it's mistakes when you convert each raw image.