OptionalcolorInitial sky colour, copied as linear-light RGB. A CSS string is parsed
as sRGB and decoded first (§60a). Defaults to white [1, 1, 1].
OptionalgroundInitial ground colour, copied as linear-light RGB. A CSS string is
parsed as sRGB and decoded first (§60a). Defaults to black [0, 0, 0],
so an unconfigured light is "white sky, no ground fill".
OptionalintensityInitial HemisphereLight.intensity. Defaults to 1 — the
multiplicative identity, exactly as DirectionalLightOptions
defaults it.
Construction arguments of HemisphereLight (§68).