Question

for a substance to look red, describe how it interacts with white light

Answer 1

the substance absorbs (i.e. electron excitations that decay through non-radiative processes) all wavelengths in the visible spectrum (i.e. white light) except the wavelengths that correspond to red light. The red light is scattered and picked up by photoreceptors (e.g. rhodopsin) in our eyes where the photon energy is converted to chemical signals and processed by our brain.