PTblender is a command-line tool that implements just the colour and brightness correction functionality of PTmender (a replacement for PTStitcher). It was written by Daniel M German and is fully Open Source. A multi-platform version is now included with the pano12 library available at Sourceforge.
Usage is like so:
PTblender [options] <tiffFiles>+ Options: -o <prefix> Prefix for output filename -k <index> Index to image to use as a reference (0-based)