Art Nouveau is high in key: pale, luminous, and filled with optical air. The palette tilts toward cool - blues and silver-greys carry the structural weight. Chroma is kept low across all colours, producing the soft, enveloping quality that characterises tonal painting. The palette gives 34.9% of the composition to a single #FBF8E0 - a decisive chromatic anchor. The highest-chroma note - #CDB471 - appears at just 4.7%, deployed as a precision accent against the quieter ground. A value spread of 63 units gives the palette both depth and air - shadows are genuinely dark, lights genuinely light. The mid-to-high key, cool bias, and moderate chroma point to outdoor observation - sky and diffused daylight as the dominant light source.