How to match colours exactly and fill in

[cmckernan93]

what is my best way to excatly match the grey tray colours exactly and fill in in the tray on the left in the below picture?

I tried a eyedropper and used a layer overlay in a new layer but I want the exact grey of the tray with label B on it so they match

[c.pfaffenbichler]

One option: 

• CVolor Sampler Tool to determine the color

• Curves Layer with the appropriate Layer Mask

• cmd-shift-click to determine a corresponding point 

• adjust the three Channels accordingly 

• if necessary adjust the Compsite Curve, too

[Trevor.Dennis]

My answer is pretty much the same, but I have tried to simplify it.

I am a big believer in the adage that the numbers never lie, so lay colour sampler points on both versions, and move the Info panel into a convenient position.  The tray on the right is pure grey, whereas the tray on the left had a touch more red and green than blue. I like to use one curves layer to adjust the hue (which is grey in this case) and another Curves layer to adjust tone.