Objects have no intrinsic color — their apparent color is determined by what wavelengths the surface reflects under the incident light

Physically, objects absorb certain wavelengths and reflect others. The reflected wavelengths reach the eye and produce the sensation of color — but this sensation depends entirely on the wavelength composition of the incident light. A blue object under orange illumination appears black (orange contains no blue to reflect). A red object under blue light appears dark or black. Colored light reflected from one surface onto adjacent surfaces creates colored reflections that alter those surfaces’ apparent hues. The Impressionists discovered that sunlight’s local color changes throughout the day alter all object colors simultaneously — hence Monet’s serial paintings of the same subject at different hours. For generative visual artists: the same RGB geometry element will read differently under colored ambient light or HDRI illumination; in non-lit 2D work, the background acts as ‘ambient light.‘

Examples

Shader: multiply surface albedo by a color-temperature varying ‘sunlight’ vector: vec3 lit_color = albedo * light_color;. A blue albedo multiplied by orange light gives near-black — models the physics correctly.

Assessment

Explain why a red garment appears black under green light; predict how a green painting looks under sodium vapor lamps (monochromatic orange); describe the Impressionists’ core discovery about local color.