Historical clue formulations

• They're at the ends of some rainbows — 2026-07-19
• Color separators — 2026-05-09
• They have many faces — 2025-06-28
• Light-refracting objects — 2018-04-09
• Dispersion devices — 2007-07-14
• Beam splitters — 2007-01-23
• Light dispersers — 2002-08-15
• Periscope parts — 2001-08-03
• Drops of water, e.g. — 1994-10-23
• They make colorful displays — 1994-02-23