If this year's plants have grown from bulbils dropped by last year's plants, then they may have reverted to an earlier strain from which your orange lillies were developed. It's the lupins and foxgloves that have minds of their own in my garden.
Others here will be able to offer a better explanation as to how this happens.

Normally, bulbils are the same color as the plant they came off of, and take 2-4 years to reach blooming size. Did you have a lot of non-blooming lily plants last year? The white ones may have been just waiting in the wings, if you bought a bag of bargain bulbs a few years ago.