moving automobiles. It often replaced red as the color of fire trucks and other emergency vehicles, and was popular in neon signs, especially in Las Vegas and in China, where yellow was the most esteemed color. In the 1960s, Pickett Brand developed the "Eye Saver Yellow" slide rule, which was produced with a specific yellow color (Angstrom 5600) that reflects long-wavelength rays and promotes optimum eye-ease to help prevent eyestrain and improve visual accuracy. The 21st century saw the use of unusual materials and technologies to create new ways of experiencing the color yellow. One example was The weather project, by Danish-Icelandic artist Olafur Eliasson, which was installed in the open space of the Turbine Hall of London's Tate Modern in 2003. Eliasson used humidifiers to create a fine mist in the air via a mixture of sugar and water, as well as a semi-circular disc made up of hundreds of monochromatic lamps which radiated yellow light. The ceiling of the hall was covered with a huge mirror, in which visitors could see themselves as tiny black shadows against a mass of light. Fruits, vegetables, and eggs Many fruits are yellow when ripe, such as lemons and bananas, their color derived from carotenoid pigments. Egg yolks gain their color from xanthophylls, also a type of carotenoid pigment. Flowers Yellow is a common color of flowers. Other plants Rapeseed (Brassica napus), also known as rape or oilseed rape, is a bright yellow flowering member of the family Brassicaceae (mustard or cabbage family). Goldenrod is a yellow flowering plant in the family Asteraceae. Minerals and chemistry Yellowcake (also known as urania and uranic oxide) is concentrated uranium oxide, obtained through the milling of uranium ore. Yellowcake is used in the preparation of fuel for nuclear reactors and in uranium enrichment, one of the essential steps for creating nuclear weapons. Titan yellow (also known as clayton yellow), chemical formula has been used to determine magnesium in serum and urine, but the method is prone to interference, making the ammonium phosphate method superior when analysing blood cells, food or fecal material. Methyl yellow (p-dimethylaminoazobenzene) is a pH indicator used to determine acidity. It changes from yellow at pH 4.0 to red at pH 2.9. Yellow fireworks are produced by adding sodium compounds to the firework mixture. Sodium has a strong emission at 589.3 nm (D-line), a very slightly orange-tinted yellow. Amongst the elements, sulfur