A Kaleidoscope of Colours: Passion is a Red Lens inside My Head. Red (from the Latin word rŭssus – rŭbeum) is one of the three primary colours together with blue and yellow and one of the seven hues of the visible spectrum. Red is the highest arc of the rainbow and corresponds to the longest wavelength of light (6500 Å) at the heat radiation limit.
The term is used in chemistry to show organic and inorganic pigments. Important examples of inorganic pigments are cadmium red, chrome and Venetian red (or red ocher), which are respectively composed by sulphoselenides cadmium, basic chromate of lead and ferric oxide. A typical organic red pigment is hemoglobin. To this category belongs also the Congo red which is usually used to dye cotton, or as a marker in analytical chemistry.