In watchmaking, contrast is not an ornament: it's a functional variable. Without a perceptible difference between dial and indicators, a watch face serves no purpose. From the workbench, I can tell you that contrast errors are among the most difficult flaws to spot in photos and almost impossible to ignore on the wrist.
The most elementary form is chromatic: light background with dark elements, or vice versa. Dials called panda — white background, black subdials — and reverse panda — black background, white subdials — were born in the Sixties as a technical response to racing drivers' needs: maximum contrast, instant readability. The same logic applies to tuxedo dials, where the light center is surrounded by a dark ring or the reverse: the chromatic division structures the hierarchy of information before the eye even focuses. The negative display in digital watches applies the same principle: dark background, light digits.
Then there's surface contrast, which is more subtle and changes in real time. A brushed zone adjacent to a sunburst finish doesn't behave the same way at every angle: your wrist moves, light changes, and the relationship between the two surfaces never stops varying. Static renders choose a single lighting configuration; reality offers all configurations at once. This also applies to applied markers on a domed dial: they reflect at multiple angles, and no software can anticipate them all simultaneously.
Finish contrast is also used on movements. Blued screws—thermally treated—on a brushed platinized bridge are a technical contrast before an aesthetic one: the chromatic difference allows you to spot the fastener at a glance during assembly. Damask steel exploits the metallurgical structure itself: forged layers and chemical treatment reveal different tones in the same surface, without adding anything foreign to the material.
A limiting and deliberately paradoxical case is the so-called phantom effect: hands the same color as the dial, contrast reduced to a minimum, readability deliberately sacrificed for a visual effect. It's a choice I know well—it works only if an accent hand (often orange or red) restores a reference point. Without that anchor, the watch becomes unreadable.
A contrasting chapter ring — typically an outer ring of a different color from the dial — is a way to visually isolate the minute track without intervening on the central zone. Used correctly, it increases reading sharpness without increasing graphic complexity.