Charles Rennie Mackintosh is high in key: pale, luminous, and filled with optical air. Blues and teal-greys govern the palette, lending it an aquatic or atmospheric quality. The absence of saturated colour is itself an expressive choice: this is a palette of restraint and atmosphere. The dominant colour, #E8E8DB, takes 29.5% of the total area, establishing the overall mood before any other hue is introduced. The highest-chroma note - #999142 - appears at just 5.4%, deployed as a precision accent against the quieter ground. A value spread of 83 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. This is palette 4 of Charles Rennie Mackintosh's sequence - a single chapter in a chromatic story told across many works.