This tutorial is taken from Getting Colour Right by Michael Walker and Neil Barstow. Click on the book image to be taken to the title information page where you can buy a copy at 20% off the cover price.

MIxed Lighting - Localized Colour Corrections, page 3

Now it looks a bit red in the walls on the left and right of the courtyard, so we pick a midpoint in the red curve and make a very small downward adjustment using the cursor keys.

The result of pulling down the curves in two of the channels is that the image has gone a bit dark again, so we go back to the RGB curve and pull it up a bit to compensate.

We click OK and leave Curves. That's fixed the brightness and overall cast, but now we need to look at the localized colour casts caused by the mixed lighting.

The clouds in the sky are too blue. In the Hue/Saturation dialog, we select Blues and then click on a central blue tone. Then we make a big Hue shift to view the automatic selection to check what has been selected and adjust if necessary.

We put the Hue setting back to 0 once we're happy wih the selection (we fine-tune it using the + and - eyedroppers; you could also use the colour range and drop-off sliders on the colour bars at the bottom). We experiment with a subtle Hue shift, but don't like the results, so instead try decreasing the Saturation and increasing the Lightness to get a more neutral sky.