If you find an RGB image with a color cast you can very simply make a quick fix to make it look better:
1. Make sure your monitor is recently calibrated. This is very important.
2. Find the brightest area(highlight) of the image with the eyedropper and Shift Click to create a sample point.
3. Find the darkest area(shadow) and create a sample point.
4. Using curves(preferred) or levels make the highlight r245 g245 b245, the shadow r15 g15 b15.
5a. If there are no skin tones in the image find a medium gray area(mid tone) and make it equals amounts of RGB.
5b. If there is a skin tone do not worry about the mid tone as the skin will draw the most attention in the image. Make the skin tone a ratio of r200 g165 b145. These will vary depending on the darkness of the skin, but keep the same ratio. A more rosy skin would use a G value of 155 while a tanned skin would use a G value of 135.
With practice this can be done very quickly, about a minute per image. It is also a good idea to covert to CMYK before sending us the files to verify how the image will print. See other posts on how to do this.