Curly cats appeared periodically in different countries, but not everywhere cat breeders managed to pay due attention to curly cats.
For example, in Romania, it was believed that a curly cat was sick and destroyed them. But, at the end of the last century, the frequency of the birth of curly cats has increased significantly and today there are already many breeds of curly Rex.
All cats have three types of hair - this is the undercoat, guard hair and outer coat. Many Rex cats have all three types of hair, but, for example, Cornish Rex and mutation-based Herman Rex have only one type of hairline - the undercoat. It is the mutation that affects the hair follicles, causing them to grow in a wave or curl. Since all coat colors are allowed in the Cornish Rex breed, we can safely say that coat genes are in no way related to coat color.
A source: https://www.zoopicture.ru/kornish-reks/