Polarimetry is a very useful tool for determining what kind of physical processes are at work in the light source (especially for synchrotron radiation) and the distribution of magnetic fields in it: there is much more to light than just color!
Polarimetry color information superimposed on a "normal" photograph of Crab nebula creates the unusual picture below. The red color in the nebula comes from an arbitrary initial polarisation angle (we weren't able to find out yet the true polarizing angle), the green shows 45 degrees more and the blue is with the filter rotated by 90 degrees compared to the original position.
The image has been made by me (color and luminance data) and David Muelheims (polarized data), in Bonn, Germany.
And although "popular wisdom" might tell you that the human eye cannot distinguish between polarization states, it's not really true, as Haidinger found out many, many years ago :)
