Set up to Color Correct in Photoshop CS5
To produce the best possible image in Adobe Photoshop Creative Suite 5, try to avoid correcting in CMYK (Cyan, Magenta, Yellow, Black) mode. If your images are typically in RGB (Red, Green, Blue) or LAB mode (L for lightness, and A and B for the color-opponent dimensions), keep them in that mode throughout the process. Convert them to CMYK only when you’re finished manipulating the image.
Don’t forget! Press Ctrl+Y (Windows) or Command+Y (Mac) to toggle on and off the CMYK preview so that you can see what your image will look like in CMYK mode without converting it.
Set up these items before starting any color correction:
Select the Eyedropper tool (the keyboard shortcut is I); on the Options bar, change the sample size from Point Sample to 3 by 3 Average in the Sample Size drop-down list.
This setting gives you more accurate readings.
If the Histogram panel isn’t already visible, choose Window→Histogram.
If the Info panel isn’t already visible, choose Window→Info to show the Info panel so that you can check values.
Make sure that your color settings are correct.