Yes, that totally illustrates the problem with 1.2MB 5 1/4" floppies. It just doesn't apply to 3.5".
For the 3.5" version you could show a track of bits written by the HD format as a stream of dots which are completely solid red, while the weaker format from the DD drive/format gets layered on top as a roughly 70% opaque green. The red will still show through, just in a different way.