Here is the most automatic way:
http://www.revisionfx.com/products/rematch/
There are some color matching entries in this list of color correction and grading resources, including some here on the COW:
http://blogs.adobe.com/premierepro/2011/07/color-correction-and-color-gradi...
---------------------------------------------------------------------------------------------------------
Todd Kopriva, Adobe Systems Incorporated
After Effects quality engineering
After Effects team blog
---------------------------------------------------------------------------------------------------------