Really? A label on a Rubble counter is easier to see with high counter density than a counter with the level color on the edges? The color is universally recognized as building level x.
I am not saying that other solutions may be thinkable, conceivably even better. But upper level rubble is pretty rare in the average game.
In VASL, it does not make much of a difference because of the mouse-over function.
In cardboard, the rubble counter will be placed above the level counter. As there can be no rubble in different levels of a building, the level counters of levels beneath the rubble will be visible by their color-code except if you had 5/8"counters in upper fortified building locations. So, for indentification purposes, it does hardly make any difference in practice. However, color-coded rubble by level could reduce counter clutter by one 5/8" level counter which would otherwise be placed directly beneath the rubble counter.
von Marwitz