Channel Mixer

The "Channel Mixer" command lets you adjust an image by re-mixing its color channels. To use it efficiently, bear in mind the three sets of complementary colors: "Cyan - Red", "Magenta - Green", and "Yellow - Blue".

1. In case the edited image is layered, select the uppermost layer.
2. Open the "Color and Tone" dialog and apply the "Channel Mixer" command.
3. In the dialog box that opens, select the proper channel in the "Output Channel" drop menu. For example, to alter the blue-to-yellow ratio, you select the "Blue" channel.
4. Try to adjust color with the "Source Channels" sliders, keeping your eye on "Total" percentage. For example, to fix a blue cast, you reduce this value; to remove yellow, you push it over 100%.

Once the "Color Balance" dialog is closed, your correction appears in the Layers panel as a separate layer.

However, you can't edit its settings on the Adjustments panel as we do it with the regular adjustment layers.

NB Using the Channel Mixer for B&W conversion explained here.