Take ye from among you an offering unto the LORD: whosoever is of a willing heart, let him bring it, an offering of the LORD; gold, and silver, and brass, An offering - A terumah or heave-offering; see Leviticus 7:1, etc., Exodus 35:6
See, on these metals and colors, Exodus 25:3 (note), Exodus 25:4 (note), etc.