Warm and cool as spatial cues, not just mood cues
The warm-cool axis in color is physically grounded: warm colors (long-wavelength reds and yellows) stimulate the eye's focusing mechanism differently than cool colors (short-wavelength blues and violets), creating a slight focal-length difference that makes warm colors appear closer. Artists have used this for centuries to create atmospheric perspective — distant objects are painted cooler and more blue to simulate the effect of atmosphere. In UI and graphic design, the same principle applies: warm foreground elements appear to sit above cool backgrounds, and cool type on a warm background has a slightly receding, readable quality. Understanding this lets you use temperature as an additional depth signal beyond lightness and size.
