The Color Balance layer allows you to control the colors of shadows, midtones, and highlights independently. Add a Color Balance layer by clicking the Color Balance icon on the Color tab of the toolbar.
The three radio buttons are used to determine which values of the image you're changing.
When Shadows is checked, the color sliders will adjust the shadowed parts of your image.
When Midtones is checked, the color sliders will adjust the midtone colors in your image.
When Highlights is checked, the color sliders will adjust the highlights in your image.