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 2

Before clicking OK and closing the Levels dialog box, we need to adjust the highlights. Using the slider with the Alt key held down, we bring the highlight level down far enough to just catch the floor lights as they're the brightest thing in the picture (bottom right).

Now we've set both shadows and highlights in one Levels operation and the image is noticeably better already.

But it's still too dark, and there's a blue cast in the stone of the church. This cast might be affected by a tonal move, so we should lighten the image first. We select a point in the stone that has a tonal midpoint in order to set values in our Curves box by command-clicking in the image with the eyedropper.

The permanent sample point shown is for illustrative purposes only; you wouldn't actually need to place one. Instead, you would just move the mouse around and click on that point.

Next we move the curve point up in RGB to lighten the overall image.

The tone is fine, but we now want to fix the blue cast, so stay in Curves (don't click OK). In the blue channel, we pick a midpoint in the blue-ish stone in the columns at the right and pull the curve down a little.