Sanke are a white fish with red and black colouration. Sanke are one of the original koi types and make up one of the Go Sanke variety (the others being Showa and Kohaku). They are also found in Doitsu (Scaleless) varieties. The Gin Rin variety has vibrant metallic scales as in this example.
One of the more popular colour types and most Koi keepers have a Sanke or two in their collection.