The actual absorbing of light is performed by one magical molecule--retinal. As in hemoglobin, special functionality is provided by a non-protein factor which is bound by the protein (opsin). The details of structure and surface of the opsin molecule determine what wavelengths of light actually "excite" retinal. When light of the correct energy (= wavelength) strikes retinal, it undergoes a change in structure that triggers a series of events that culminate in a nerve signal.
Image sharpness (slower but prettier)