18 kt yellow gold ring with 1 diamond of approx. 0.25 ct

Yellow gold : Yellow 18K gold is an alloy contianing 75% of pure gold, whereas 14K gold contains only 58,5% of pure gold.
Color : White diamonds color range from D (colorless, the purest white) to Z (light color). D, E and F are colorless diamonds, G, H , I and J are near colorless , K and L are faint color, M to Z have a light color.
Diamond : In mineralogy, diamond is an extremely rare, precious and hard (named after the ancient Greek "unbreakable") metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice.