Color Sampler Tool (Photoshop CS4)
Sample first image. Write down RGB values.
Open Curves with 2nd image. Select the sample area in the 2nd image and Ctrl + Shift + click to take the sample.
From the drop menu select the Red channel and set the output value to the Red value written down from the 1st image. Repeat for Green and Blue Channels.
|Ruby Red Dress by cjf2|
from High key portrait with RED
|Follow me home by eaa|
from Shades of Blue in Nature