Function theme 

pub fn theme(ui: &Ui) -> Theme

The theme stored on the ui’s context (or Theme::default if none).

Readable-data side effect (LAW 6): every call records the palette it hands out into the probe thread-local, so a headless test can read back which palette a component actually consumed during its paint — proof the component read the active theme rather than a private default. theme(ui) is the single universal consumption point for every custom-painted facet, so instrumenting it once gives uniform, per-component palette-consumption evidence.