[PyMOL] Color by RMSD

Hi!

I want to color the cartoon of a protein that has been aligned to 
another protein where the color changes as the RMSD changes. My python 
programmer husband is helping me by adapting Robert Campbell's 
color_b.py script but I am not sure where to get the RMSD values. I was 
thinking intra_fit, or intra_rms or intra_rms_cur would work because 
they return an array which could be used but it is not clear to me how 
they work. I don't see where to put the two sets of atoms; rms and fit 
have the seemingly correct input but don't return the array, right?

Thanks for any clues.

Cheers,
Holly