Pure gold is slightly reddish yellow in color, but colored gold in various other colors can be produced. Colored golds can be classified to three groups: Alloys with silver and copper in various proportions, producing white, yellow, green and red golds; typically malleable alloys Intermetallic compounds, producing blue and purple golds, as well as other colors. These are typically brittle but can be used as gems and inlays Surface treatments such as oxide layers Pure 100% gold is 24 karat by definition, so all colored golds are less than this, with the common being 18K (75%), 14K (58%), and 9K...