Quote - > Quote - All anti-gamma is the same.

Color_Math:Pow node
Value_1 = your incoming color, or white and connected to your incoming color
Value_2 = white - connect to 2.2.

NOTE:EDITED CORRECTION I WROTE THE WRONG FACTOR Value_2 should be 2.2

like this? 

but can we have then the color in the preview?

p.s. so all the time we rendered the wrong colors?

That is the correct setup. Not "wrong" colors, per se, just that whatever color you wanted you had to put a much more saturated color into the light.  You couldn't just pick the color based on looking at it.

Now you can.

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