Here is Thor's Helmet (NGC2359) before levels adjustments:

Notice how the Red is further to the right as compared to your Green, and Blue channels. This is not a color balanced image. To balance the color you need to move the Red Histogram to the left.

Here is the same image after applying Red Levels:

Notice how the TOP RGB is one bell curve, and there is not a second peak. Lining up each color channel is easy to do in Levels.

In this particular case in PHOTOSHOP, select IMAGE-->ADJUSTMENTS-->LEVELS. From there a Levels window will pop up. From the CHANNELS pull down menu (in levels) select the RED CHANNEL. We only want to move the RED channel. Take the BLACK SLIDE KNOB under the Histogram and MOVE IT TO THE RIGHT. As you MOVE the BLACK SLIDE KNOB the histogram peak for the RED will move....try to align the RED closest to the CENTER of the other color channels.

The example I created I only applied the RED LEVEL adjustment. As you can see this has dramatically improved the color balance of the astro image.

Let me know if you have any questions.
OR
If you would like to expand on this tutorial...Please do!

Doug

I hope this tutorial was helpful, and if anyone knows a better way…please share!