I tried extracting the icons from the EXE using resource editing, but couldn't do so successfully, so I created my own set.
These allow me to see the difference between "Excellent", "Very Good" and "Good". Grey seemed to be appropriate for "Average", so I left it alone.
I hereby put them into the public domain. I'd insert them into my EXE of ImgBurn, but can't figure out how.
EDIT: I just noticed, I accidentally changed the intensity of the grey. I've attached a new grey icon which closer replicates the original.