The best color correction is of course done when you have the RAW file. You can tweak the WB to your liking without destroying information - that's one of the most important revolutions of the digital era of photography. Most take Auto WB for granted most of the time.
Manipulating the RAW file can give you any color you need even after the photo is taken. You can even experiment with White Balance to see how different settings affect the mood of the photo.
Using a JPEG instead of the RAW file, it happens. Sometimes we just have the copy not the original. But you still need to correct the color, first you must identify the problem to correct it.