Here is the British Cavy Council's description - “Guide Standards are defined for breeds of cavy that are in a process of development but that, in the Council’s opinion, represent varieties that are distinct from all other existing breeds, are likely to provide a desirable addition to the Cavy Fancy, and for which a provisional standard of excellence can be stated after an initial period of breeding and exhibition under the auspices of a Specialist Breed Club."
Accepted breeds are the: Tricolour, Bicolour, Chinchilla, Swiss, Harlequin, Magpie, Argente, Solid Argente, Lunkarya and Californian.
This now includes the Tortoiseshell.
The Chinchilla has a new Guide Standard from January 2018 and new colour names. Here are photos of the 4 accepted colours and the updated Guide Standard.
It is considered that a judge knows the Argente Guide Standard and Solid Agouti Standard and hopefully has the competence to combine the two, so the link will take you to the Standard for the Solid Agouti.
Argentes have for now been moved back down to a Guide Standard from January 2018. They now also come in Slate based colours.
The Californian has been given a Guide Standard from January 2018. This is only for the Chocolate and Black pointed Californians in English Self CC colours. Pink eyed Californians with Lilac or Beige points remain a New & Emerging breed.