Icons: intelligently invert icon colors in dark mode

[anandpant]

Problem

icons.sketchi.app has a light/dark preview toggle, but the icons themselves are not adapted — they are rendered as-is. Many brand marks are monochrome black (or near-black) and effectively disappear against a dark surface; a few are white-on-transparent and disappear against light.

Naive CSS filter: invert() is not acceptable: it would wreck multi-color brand marks (Google, Slack, Firefox) and change brand colors, which is both ugly and a trademark-usage problem.

What "intelligent" needs to mean

Some classification per icon, likely precomputed in the manifest at build time rather than at render time:

• Monochrome dark — safe to invert or recolor to currentColor in dark mode.
• Monochrome light — safe to invert for light mode.
• Multi-color brand mark — never recolor. If contrast is insufficient, put it on a neutral chip/plate instead of touching the artwork.
• Has its own light/dark variants — some brands ship both; prefer the official variant.

The manifest already carries per-icon metadata (aliases, keywords, viewBox, bytes), so a colorMode or contrastStrategy field is a natural addition, computed by the icon pipeline.

Open questions

• Is per-icon classification derivable reliably from the SVG source (count distinct fills/strokes, detect near-black/near-white), or does it need review?
• Should the same metadata be exposed through /api/icons so agents and downstream consumers get it too? Probably yes.
• Does this interact with #288 — logos inside diagram nodes will hit exactly the same problem once diagrams have dark backgrounds.

Priority

Future state. Raised by the product owner as a desire, explicitly not urgent, because the difficulty is unknown until the classification approach is proven.