Shooting RAW is a good way to combat the effects of incorrect white balance either due to settings or funky lights that throw the auto white balance off. The problem is, sometimes RAW is not an option. This lesson will go over manually adjusting the histograms (if you don't know how to read histograms or don't understand them, read this) in different color channels to correct a jpg that has an incorrect color cast (too red/warm or too cold/blue).
This technique can also be applied to curves. 
TIP!! You can apply your adjustments two multiple images in two ways.1) Record an action and create a droplet or set a hotkey!
This allows you to quickly manipulate many images in the same way. For example, if you set the action's hotkey to F2, the next image that comes up with a similar color cast, you can just hit F2 to apply the level adjustment. This is GREAT if the color cast changes between photo to photo. If your images are all a similar cast, creating a droplet and batching your photos will probably be more effective.
2) Save your levels and LOAD them for another image!
Tip!!
Larger Sample
Using the eye dropper tool on a single point is risky because of color noise. Theres a strong chance you'll randomly click on a point that deviates from the average color more than the others. Because of this, it is wise to use a larger area to sample from by using a 5x5 average point instead of a single point. Just right click with the eye dropper tool and go down and click on 5x5!
*bowdown*