Merle is a color often seen in Australian Shepherds, and while it may be a very striking color, it only comes naturally in a few breeds. The poodle is not on that list. You may stumble upon merle poodles, but these dogs are not true poodles, they are mixes. This color was "created" by puppy mills who wanted to sell exotic looking puppies for big bucks. They achieved this by breeding merle colored dogs to poodles and crossing them back to poodles until they looked "purebred." And because merle is a dominant gene (only one parent needs to be merle to produce the color), it was very easy for these puppy mills and backyard breeders to create a purebred looking mutt with the merle color, and make lots of them. These merle poodles may have been AKC registered, but they were dishonestly registered (a different sire was used than what is documented in the pedigree).
Breeders who breed merle poodles are either ignorant of what they are doing, not caring to do proper research, or they know what they are doing but just don’t care. Whatever they may claim, it is dishonest to call these dogs purebred and dishonest to register them. There are also many health problems linked to this color including blindness, deafness, skin cancer, sun sensitivity, and even deformed or missing eyes and ears. No merle poodle breeder is a reputable breeder, they breed only for color and money, not for health, not for conformation, and most definitely not to improve the breed in any way. And if you ever stumble upon an exotic looking color in another breed, always question it and do your homework!
Here is a list I made of AKC & UKC recognized breeds that come in the merle color:
American Leopard Hound, Australian Shepherd, Bergamasco Sheepdog, Beauceron, Border Collie, Cardigan Welsh Corgi (not Pembroke), Catahoula Leopard Dog, Chihuahua, Collie, Dachshund, Dunker, Great Dane, Miniature American Shepherd, Mudi, Old English Sheepdog, Pomeranian, Pyrenean Shepherd, and Shetland Sheepdog.
You can also use this tool to find a list of colors for every breed in the AKC.