Visual appearance of objects comes from the interpretation by the human visual system of a light signal issued from the objects. Describing or predicting appearance is therefore a question of light and requires notions about light propagation and measurement. In this paper, we introduce basic laws of optics, the science of light, and radiometry, the science of light measurement, in the context of colored surfaces. We address light spectrum and illuminants, polarization, notions of reflectance and transmittance based on radiometric definitions, gloss, absorption, scattering, fluorescence and models for light reflection and transmission by flat and rough surfaces, by slabs of nonscattering media and diffusing layers. Throughout the paper, we present the most current methods to assess the different physical quantities by measurement.