The first Macintosh drew everything at one bit per pixel on a 9-inch, 512×342 screen. There was no grey in the hardware, so every tone you remember — the desktop, the scroll bar, the disabled menu item — is a pattern of black and white pixels.

This system keeps that discipline: white window interiors inside 1px black frames, six-stripe title bars, Chicago-style capitals snapped to the pixel grid, and Susan Kare's 32×32 icon craft. Edges are hard, shadows are a single pixel, and grey is always a dither.