Good post (above).
Yes, color is important. I only have gray orange and yellow.
I wish I had grasshopper tan and green drake olive too.
Maybe even black.

That's why I've been ranting. Maybe some fly tying materials
distributor will finally get smart, and buy the right stuff.

Good luck with machining lightweight poppers.
Seems like you might need a styrofoam, because of its rigidity.
One last thing nobody has mentioned yet:

in general, the smaller the gas bubbles, the lighter the foam,
if the bubbles are both small and tightly packed, that is.
(foam has an opposite relationship to buckshot in a mason jar,
if you think about it).
So maybe you want a styrofoam of some kind, with microscopic gas bubbles.