Yamaha really made this statement:

Glossy black piano finish provides improved signal-to-noise performance



I thought I would seek opportunity to hear these speakers, but now I do not think so






Yes, from the record all the way to the speakers there is MUCH great engineering, designing and manufacturing that brings us the great sound we love and keep's us coming back for more!!
Some comments can easily compete for award in utmost nonsense:
" All six external surfaces of the enclosure have a glossy black piano finish created using the same dedicated paint, primer, and polishing processes used for Yamaha’s renowned grand pianos. The uniform and hard membrane further increases the overall rigidity of the enclosure, and at the same time it suppresses fine vibrations, contributing to the bright sound and significantly enhanced signal-to-noise performance."

Audio Machina (no relation to your humble scribe) builds speaker cabinets from solid billets of aluminum and Rockport is no slouch at speaker cabinet building, applying shipbuilding engineering principles to speaker cabinetry. The Rockport Hyperion tips the scales at 500 lbs per side. That’s a lot of inertia, gentle readers.

Speaking of Robert Harley, the best stereo system he ever heard is.....

Unimportant as it is, but I do suspect that these Yamaha speakers from the OP actually sound quite good. I have no knowledge, but think they might be charging money for something.

Now, is paint contributing to it or not, I have even less of an idea but I would cut them some slack.
I fail to see why paint can't affect sound but backward wires and magic mats in the mains panel box can.