This script simulates a photochrom image, a lithographic printing process from the 1890’s:
http://en.wikipedia.org/wiki/Photochrom
The script is a translation of this how-to for PSE with some improvements:
http://www.alibony.com/pse/031508postcard.html
Copy it into the scripts folder from GIMP, you will find it then under Filters → Artistic → Photochrom.
If you like it, hug someone.
Examples:
https://www.flickr.com/photos/28653536@N07/4390570531/
https://www.flickr.com/photos/28653536@N07/4394791509/
Updates:
gimp -i -b '(elsamuko-photochrom-batch "picture.jpg" (list 255 128 0) (list 255 68 112) 60 60 0 100 FALSE FALSE)' -b '(gimp-quit 0)'
gimp -i -b '(elsamuko-photochrom-batch "*.jpg" (list 255 128 0) (list 255 68 112) 60 60 0 100 FALSE FALSE)' -b '(gimp-quit 0)'