How do I adjust specific colors in my photos (HSL / color channels)?

Open the photo in your listing gallery and go to the Basic Adjustments tab. Scroll down to the Color section to find colored circles for each channel (Reds, Greens, Blues, etc.). Click the circle for the color you want to adjust, then use the Hue and Saturation sliders.

Example: toning down greens

Click the green circle and lower the saturation, or shift the hue to make it less vibrant. Hit Save when done.