Ok, I have now looked at what JA wrote, and there is much that I like about that. However, I also realized a rather critical point that EG made: The threshold isn't the color, it is between the colors. I think the user would expect to add a threshold and color as a single step, and that works for most situations. The threshold becomes the bottom edge of the color, in effect, so that values above that take on the color. I think that is how most people would expect it to be, but there could also be one color below the lower threshold...or not. I really don't want to have the user add the thresholds, then color the regions between the thresholds. I think I can make that appear pretty reasonable to the user in my design, because I can adjust the text on the colors to more clearly indicate what they are displaying. I might do a mash-up of a couple of the designs.

But first, I've taken too long and will be doing lunch.