Context: Together with caesium and gold (both yellow), and osmium (bluish), copper is one of only four elemental metals with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells is such that it corresponds to orange light. The same mechanism accounts for the yellow color of gold and caesium.

Question: How many metals have a natural color that isn't gray?
Answer: four

Question: What color is pure copper?
Answer: orange-red

Question: What does copper aquire when exposed to air?
Answer: reddish tarnish

Question: The energy difference between filled 3d and half-empty 4s atomic shells corresponds to what color of light?
Answer: orange light

Question: What color is the metal caesium?
Answer: yellow

Question: How many grains of sand have a natural color that isn't gray?
Answer: Unanswerable

Question: What color is fake copper?
Answer: Unanswerable

Question: What does copper glow when exposed to air?
Answer: Unanswerable

Question: What color is the planet caesium?
Answer: Unanswerable