A very large proportion of common goldfish breed true to type, which makes this fish good for beginners, but it is a difficult fish for showing because it is such a relatively simple fish (which makes it difficult to develop a strain that stands out above the ordinary); intensity of colour is the key to doing well at shows.
Young fish are very dark, if not black, and gradually develop the ornamental red (or orange, etc) colour over 1-2 years.
The common goldfish is metallic, either self-coloured or variegated.
The calico version of this fish is called the London shubunkin and has the same body and fins as the common goldfish.