The reason they appear white is due to a recessive gene that causes a lack of pheomelanin, the pigment responsible for orange and yellow coloration. This lack of pheomelanin leaves only eumelanin, the pigment responsible for black coloration, resulting in the white base with black stripes.
It's important to remember that white tigers are not albinos. Albinism is a complete lack of both pheomelanin and eumelanin, resulting in white fur and pink eyes. White tigers have blue eyes because the lack of pheomelanin also affects the pigmentation of the iris.
So, while white tigers might look cream-colored in some lighting, they're actually a very light shade of orange with black stripes, caused by a genetic mutation that affects their pigment production.