The document discusses additive mixing of colored lights and some key properties: 1) We can match a wide range of colors using mixtures of primaries like red, green, and blue lights. 2) Grassman's law from 1853 states that stimuli of the same color will produce identical effects in mixtures regardless of spectral composition. 3) Modern colorimetry is based on experimental properties of additive mixtures of colored lights established over a century ago. Subsequent experiments have refined the conditions where simple laws hold.