Grade Color Matching in Nuke.

example to match the foreground color range (un corrected) to background color range (corrected).

Controls:-
When matching colors, the normal operation is to match black and white points between the foreground and background (only changing the foreground), and then match the level of the midtones gray, and finally match the midtone hue and saturation.

To find max and min points in the image use, curve tool set to Max Luma Pixel and hit go !! 

blackpoint:- value of darkest point in the foreground(un corrected).
whitepoint:-value of brightest point in the foreground( un corrected).

Lift:-min value of background (corrected)
Gain:-max value of background (corrected)

Now use, multiply and gamma to match the midtones, in the image and cc the mid tone.