I want to discuss the specific challenge of painting light in difficult conditions: overcast light, fog, deep shadow, and other scenarios where the usual 'warm light, cool shadow' logic doesn't straightforwardly apply.

Overcast light: the sky is the light source in all directions. There are no hard shadows. The light is soft and even. Values compress toward the middle of the scale. This is actually a useful lighting condition because without harsh shadows, surface color and material quality read more clearly.

Fog: objects lose contrast and saturation as they recede. Near objects have their full material quality. Far objects are desaturated, lighter, and blue-shifted. Fog essentially pushes the atmospheric perspective effect to an extreme.

Deep interior shadow: the darkest darks in a daylit interior are still usually not pure black — they have the color of the ambient light that reaches them, which is often blue skylight from windows. Absolute black exists almost nowhere in natural lighting.