Explicit background for passes that clear the frame (e.g. RenderPass and
the OIT opaque clear). When set, the pass clears to this colour/alpha instead of
the renderer's current clear state, giving a single source of truth so the
background is identical regardless of which base pass renders the scene. When
null the pass falls back to the renderer's current clear colour/alpha.
Explicit background for passes that clear the frame (e.g. RenderPass and the OIT opaque clear). When set, the pass clears to this colour/alpha instead of the renderer's current clear state, giving a single source of truth so the background is identical regardless of which base pass renders the scene. When
nullthe pass falls back to the renderer's current clear colour/alpha.