Five grayscale (black->white) sliders in Preferences that update live:
outer-chrome background (QPalette.Window), the rounded transport button
boxes, the now-playing panel, the now-playing text, and the row stripes
(QPalette.AlternateBase). Defaults are None ("inherit current") so nothing
changes until the user drags. Decouples the button boxes from the stripe
color (they used to share palette alternate-base). Live preview via
Preferences.set_live (no disk write); persisted ~0.4s after the drag.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
