Refining Colour Contrast with a Black & White Adjustment Layer!
Try this easy method for adjusting colour contrast in your image. The 1st screenshot shows the original image.
The 2nd screenshot shows a Black & White Adjustment Layer. Changing the ‘colour’ saturation sliders will alter how the distribution of black and white pixels in areas that were originally that colour. For example, here I have brightened cyan and the corresponding pixels in the greyscale image are made whiter.
In the 3rd screen shot I have set the BW Adjustment Layer to Luminosity Blend Mode. You can experiment with different Blend Modes and add Layer Masks to refine the effect.