If some superballs are manufactured with varying grades of elasticity then it should be trivial to get a gradient bounce out of the correct drop setup. The superballs would all be the same size.
I'm am thinking a red superball, long wavelength, so the softest elasticity right through the rainbow colours
to a violet superball, short wavelength, with the strongest bounce.
A downward roll off a cliff edge onto a 45 degree plane would be a nice effect for 1000 or so mixed balls.
But what would be setup to get the rainbow out of a large height drop already bouncing mixture? Any suggestions? **
The impetus being, if the experiment is to drop 20,000 superballs from a helicopter for a demonstration to excite interest in science, why not add some of nature's quirks.
** maybe a big angled paraboloid. More science.