From the Resolve 8.2 manual p251:
Using the RGB Mixer with “To monochrome” turned on gives you the ability to mix your own custom blends of all three color channels to emphasize the creative characteristics you require. For instance, increasing the mix of blue and decreasing red and green can give skin tones a darker, metallic sheen. The following screenshots show multiple versions of the same image with different monochrome mixes.
And this is basically what you are asking about.
It's a real fun tool!