How to use only the luminosity of the environment texture but without color influence? Sometimes, environment textures are good to give a more realistic look to the rendering.

But, it may be hard to tune the colors because of it :


Blue sky visible on the top right part (from the environment texture)
Greeny sand (which is normally more yellow) on the bottom part




Is it possible to have the lighting only on the mesh objects (no color influence, only the light strength), but keeping the colors in the background ?
I think this setup will work. It desaturates the image that will light the scene, but the original image will be visible to the camera.



A different version suggested by JtheNinja. I also needed substract node to switch 0 and 1, and multiply node to control the strength of light.