A rough rule of thumb, to color correct most images in postwork, is to make sure that the darkest part of the image is pure black, the lightest part of the image is pure white, and that shades of gray have no other colors mixed in. Photoshop's levels and curves have three eyedroppers that do just that. Clicking in the appropriate parts of the image with those eyedroppers often gets pretty close to the correct colors in the image. Sometimes clicking with the eyedropper will produce an undesired result, but CTRL-z usually reverts it to its previous state and cancelling will get rid of all changes done in curves or levels if things are going too bad.

What this is basically doing is establishing a dynamic range in the image. An image without a pure black or a pure white often looks dull or muddy because it lacks good contrast. If an object, that is supposed to be gray, isn't, then there is a color cast to the image. Making the gray object  gray will often get rid of the color cast.

As with everything, there can be exceptions because not all images are alike. Some images don't have anything that ought to be pure black or white. Others have an intentional colorcast.

With the original image of my underwater cave scene, the darkest black is a dark gray and the lightest white a light gray. By forcing the darkest black and lightest white to pure black and white, the figures pop out of the background. Increasing the blue channel in Photoshop got rid of the yellow colorcast in the original image (yellow being the opposite of blue light).

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon