Function scene_metadata_colors_json 

pub fn scene_metadata_colors_json() -> String

Every record carrying an imported COLOUR, as {name: "#RRGGBB"}.

The narrow read the display layer needs. It exists because this store is THREAD-LOCAL to whichever thread ran the history: BREP_render executes a run on a background thread / worker, so anything the main thread wants must be read runner-side and shipped in the RunOutput (the same reason the assembly pose write-backs are read there). See io/appearance.rs for the record convention and BREP_render/src/pipeline.rs for the consumer.

Deliberately colour-only rather than a whole-store dump: every face carries sourceFeatureId and friends, and pushing all of that across the seam into the caller’s own metadata store is a different decision from “an imported colour should be visible”.