What are gray and white cats called?

Gray ('grey' in the UK) and white cats are called 'bicolor cats' (two colour cats: gray or another color and white!). Sometimes people refer them as 'solid and white'. Solid and white applies to all colours and to shorthair and longhair cats. Gray and white describes a cat coat type not a cat breed. Many cat breeds are allowed under breed standards to have gray and white coats such as the Scottish Fold shown below.

Gray and white cat which happens to be a Scottish Fold but the coat applies to any cat, purebred or moggie. Photo in the public domain.