Feature 108 (US6, FR-017): the theme mode the live-theming primitive resolves against. A closed Controls-local DU (Light | Dark) — deliberately NOT `FS.Skia.UI.Color.Palettes.RampVariant`, so `Theming` adds no Controls→Color package dependency (the plan's "no new dependency" constraint). The WCAG contrast reuse (`FS.Skia.UI.Color.Contrast.ratio`) is exercised in the Controls.Tests theming suite, which references the Color package directly (test-only, no package impact). Placement note: the `RolePalette`/`Theming` surface lives in the CHILD namespace `FS.Skia.UI.Controls.Theming` (not the contract sketch's bare `FS.Skia.UI.Controls`) so its role field names (`Background`/`Foreground`/`Accent`/`Danger`/`Muted`) are not auto-in-scope during `Control.fs` compilation, where they would otherwise poison `Theme` record-field inference (the documented "type-move clashes Theme fields" gotcha). Consumers `open FS.Skia.UI.Controls.Theming`.