A white panther may therefore be a white puma, white jaguar or white leopard.
Of these, white leopards appear to be more common although still very rare.
Unlike black panthers, they have not been selectively bred. White panthers may be the result of albinism, leucism or the chinchilla mutation.

-From Wikipedia

A wild-caught albino leopard called Jinx was apparently kept at the Central Park Zoo, USA between 1935-1960 and had originated from Mozambique. Descriptions suggest the markings were visible in certain light. White leopards were apparently born at Los Angeles (USA) Wildlife Weighstation; these were leucistic i.e. white but with normal colour eyes. They developed spots as they grew older.
During the 1960s, one of two cubs born to a pair of normal spotted leopards at Colorado's Cheyenne Mountain Zoological Park was pure white, but apparently turned black by 5 months old. In May 1978, a pair of white leopard cubs were born to normal (spotted) leopards at Rome Zoo. Both had to be hand-reared. The male cub was whitish with light grey spots and died shortly afterwards due to internal abnormalities. The female survived and was snow white in colour. As she grew older, her coat turned pale grey and the spots became visible.
A 1993 issue of the Journal of the Bombay Natural History Society contained an article listing 11 instances of albino, or partial-albino, leopards noted between 1905 and 1965. Most are from the Bihar and Madhya Pradesh areas of India. Unlike melanism, albinism would make a leopard more conspicuous and a less successful predator. Being both unusual and conspicuous, albino leopards would have fallen victim to big game hunters' guns.
A white, but apparently not albino, leopard cub born in Africa was sold to a zoo in Japan in the spring of 1999 and is called "Nana". Two leopard cubs were born at the Wildlife World Zoo in Arizona; one, named "Isis" was believed to be the only white leopard to be born in captivity. Several experts confirmed that she has white skin, though she was also described as having spots. Blood tests on Isis and her parents were planned if she thrived and if her skin remained white. Claws 'N' Paws Wild Animal Park, Pennsylvania also claimed a white leopard

-From Wikipedia

Ghost jaguars have been reported in Paraguay, South America. They have greyish white fur with faint markings on the flanks.
Albino jaguars with almost invisible markings have also been reported. Albino and partially albino jaguars have been reported from Paraguay.
Spanish soldier-naturalist Don Felix de Azara described a jaguar so pale that its rosettes were only visible in certain lights. This corresponds to the pattern found on albino leopards . Rengger described a greyish white skin with faint shades of markings on the belly and flanks, the claws had been white according to the hunter who shot the animal.
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A white puma has been photographed. It was not albino but was leucistic (white, but with pigmented skin and pigmented eyes).
A white puma was reported several times in 2001 at Red Rock Canyon National Conservation Area and was identified from photographs and reports as an albino puma.
-From Wikipedia