I have used varnish on black colored tweaks for the past decade. Different colors give a different sound signature. The neutral colors are white or black. White has an open and transparent sound while black has a blacker background, but also dark, muddy and veiled sound. By using varnish on top of black paint you compensate for the veiled sound and add clarity. This gives good balanced sound.
Unbelievable
Yamaha really made this statement:
Glossy black piano finish provides improved signal-to-noise performance
https://europe.yamaha.com/en/products/audio_visual/speaker_systems/ns-5000/index.html
I thought I would seek opportunity to hear these speakers, but now I do not think so