RGB color model spaces for more details. The choice of primary colors is related to the physiology of the human eye; good primaries are stimuli that maximize the difference between the responses of the cone cells of the human retina to light of different wavelengths, and that thereby make a large color triangle. The normal three kinds of light-sensitive photoreceptor cells in the human eye (cone cells) respond most to yellow (long wavelength or L), green (medium or M), and violet (short or S) light (peak wavelengths near 570 nm, 540 nm and 440 nm, respectively). The difference in the signals received from
Helmethead gecko are flattened and spatulate. Helmethead geckos can be anywhere from light grey to dark brown, either uniform in color or with pale or dark blotches. The underside of the gecko is light-colored. This gecko is mainly nocturnal, and whereas most lizards are diurnal and have lost the rod structures in the retina that is typical of vertebrates, retaining only cones, this gecko has further adapted its eyes so that it has some degree of color vision at night. The gecko has developed a multifocal optical system which enables it to distinguish between light at different wavelengths. The pupils of this