Image -> Adjust -> RGB Curves...
This allows you to apply nonlinear correction on separate RGB channels.You can immediately see results on image and on Tone Curve.
With RGB Curves you can adjust the image color tone. The correction
has similar characteristics as a gamma for the values <1.0
enhancing contrast in the shadows for each channel.
For the values >1.0 the curves have (1-gamma) characteristic enhancing contrast in highlights (unlike gamma which decreases contrast in bright areas).
You can lock all sliders with the All together check box. Then all channels will have the same value. On some images values >1.0 may work better than Gamma adjusting, because the image would enhance its contrast in bright areas.
|Moving all sliders into the right (All together) will enhance contrast in bright areas.|
|The original image had a blue cast. We can remove it by moving the red slider to 1.5 and Blue down to 0.8|
|We can create an interesting color creations. R-0.4,G-1.2,B-0.2|