@dday9, in my opinion that looks much better than your first try. It's basically the same as mine but with a different orientation of the list itself. The only issue I have with it is that you can't see what the actual threshold values are, unless you click on it and select the value option in the popup menu. Maybe the value should be printed inside the colored squares, in which case it's almost exactly the same as my idea with the exception of the orientation (and for the obvious fact that it doesn't utilize a regular listbox, the advantage of using a listbox is that you get the scrollbars for free but that might not matter in this case since you probably don't need them).