Thank you!
I mentioned in my first question that I had trouble with pcolor, but maybe I can get it to work the way I need if I write a custom colormap with 6 entries. I haven't played with colormaps much, so I'm not sure if it'll work, but I suppose it's worth a shot.
imshow would be good if I could control the axes. I definitely need to have a set of coordinates to go along with the plot, but I didn't see anything about that for imshow in the documentation. Since it's meant for image processing, I didn't really expect anything, though.