Drawing.PartColors (a public array aliasing the active scheme's), Drawing.UseGoldenAngleColors and a non-atomic colour counter were process-global display state. PartPalette now holds a copy of the colours and the golden-angle flag; PartColorPalette.Current/Use swap it as a whole, Drawing.GetPartColor/GetNextColor read it, and the counter increments atomically. Colours shown are unchanged.
Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
