Oftentimes it might be a bit tricky to achieve the right White Balance, especially when shooting jpg. I usually shoot RAW and try to get the color temperature as close as possible in Adobe Camera RAW or Lightroom.
For this tutorial I purposely introduced a slight yellow-ish warm cast to the image. Oftentimes, it’s hard to find a neutral spot for using the mid-gray picker in the curves or levels… the goal is to make this image as neutral as possible with the least amount of work.
First we make a duplicate via “duplicate layer”:
which should look like this:
now, select the top layer and run the Filter>blur>average filter, which gives us some ugly looking brown mess like this:
now we make a curve adjustment layer:
take the neutral color picker (the middle one) and click anywhere in the brownish area
(marked with the X) – voila, your brown shows as neutral gray:
here how this simple move applies to the RGB channels without me (or you) touching a single curve:
now you can simply deactivate (or toss) the middle layer to see the final result – pretty cool, huh:
The easy way out: If you go into the curves “options” dialog you’ll find a “Snap Midtones” option which works almost (but only almost, depending on the image) as good: