The arrangement of outer electrons around the gold nucleus is the reason for the yellow color; to be precise, the transition of electrons from the d band to unoccupied positions in the conduction band.
Finely divided gold, like other metallic powders, is black; colloidally suspended gold ranges in color from ruby red to purple.Gold can mixed with other metals to give it different colors.
White gold is very popular right now. It can be in 18-karat or 14-karat gold (but not in 22-karat, as it is yellow gold). There are two basic types of white gold alloys: white gold mixed with nickel and white gold mixed with palladium. Nickel can be mixed with gold to create a white or gray color, but some people have an allergy to nickel. Palladium is another metal used to create white gold. Palladium is better but it costs more. To enhance the whiteness, almost all white gold is plated with rhodium, a shiny, white metal which is extremely hard. Depending on the amount of wear to a piece of jewelry, over time this rhodium plating may wear off, revealing the original metal color.
Copper creates pink and rose tones in gold.The more the copper, the deeper will be the effect.
Greenish shades are created by adding silver to gold while excluding copper from the mix. 18K green gold can be made from 75% gold and 25% silver. Cadmium can be incorporated to vary the tint of green. So combining 75% gold and 23% copper with 2% cadmium creates a light green, while 75% gold, 15% silver, 6% copper and 4% cadmium creates a dark green.
Rose gold and Green gold can be 18-karat or 14-karat but the color is stronger in the 14-karat alloys.
Purple gold. It is referred as amethyst or violet gold. Purple gold is obtained by mixing gold and aluminium in a certain fixed ratio. Gold content is almost 79% and therefore it is qualified to be referred to as 18K gold.
Blue gold is made as an inter-metallic compound between gold and indium . The gold gets a bluish hue color with this process.
Black gold is created using a few techniques. Electro-deposition using black rhodium or ruthenium is the first technique. Controlled oxidation of Carat gold containing cobalt or chromium can also be made to create black gold. Amorphous carbon is also used some times, with the Plasma Assisted Chemical Vapor Deposition process.
Chocolate gold is derived from a relatively new method created in Italy. Referred to as physical vaporization and deposition, it entails placing gold (usually rose-colored) in a suction compartment and blasting it with electrodes. This approach causes the gold's surface to oxidize in a controlled environment, resulting in the metal's color changing at a molecular level and producing a rich chocolate color. This permanently alters the metal and can only be removed by scraping off the outer layers
ALLOY NAME & COMPOSITION
Blue Gold 18K
Yellow Gold 14K
Yellow Gold 18K
Yellow Gold 22K
Green Gold 18K
Red Gold 18K
White Gold - 14Kt
White Gold - 14Kt
White Gold - 18K