The answer to this was actually in the colormap... something that's very hard
to futz with unless you're using xv or some other similar product.
If you look at the colormap as a 16x16 grid (as shown in xv) and you look at
each color component separately (an easy way to do this is to set the gamma
value for a single component to 1000 and set the gamma value for the other two
components to 0) you get:
Red - SHO
Green - EPR
Blue - INT
For an answer of shoeprint.
Contact: MIT IAP Mystery Hunt -- puzzle@mit.edu