John Singleton Copley is low-key throughout, a quality associated with Nocturnal Sienna - deep shadows dominate the composition. Heat pervades this palette; warm chromatic identities outweigh cool ones at almost every weight. Muted throughout, the palette achieves its effects through value and temperature rather than chromatic force. John Singleton Copley gives 38.0% of the composition to a single #161415 - a decisive chromatic anchor. The highest-chroma note - #70422F - appears at just 6.3%, deployed as a precision accent against the quieter ground. At 74 units of value range, the palette has the tonal breadth to sustain complex spatial readings. The combination of low values, muted chroma, and compressed range is the signature of the Tonalist mode - painting as atmosphere. Palette 5 sits within the larger chromatic argument that John Singleton Copley's complete body of work advances.