I had to do a double take when this flower opened. While this was unexpected, it was not unprecedented. There is a photo of a similar plant on the website of the Pacific Bulb Society that shows a similarly colored plant that originated in the Florida panhandle (http://www.pacificbulbsociety.org/pbswiki/index.php/NorthAmericanLilium#catesbaei).
While the Florida plant is quite showy and similar, it differs from my seedling in that the petals are more narrow, and there is a complete absence of spotting. Whatever the differences are, they are both exciting plants and are monumentally rare, as is any form of L. catesbaei, in collections.
One more photo comparing a typical L. catesbaei and the aberrant cream-colored seedling.
There is one slight "problem" with Lilium catesbaei. Based on my experience with the species, it appears to be monocarpic. So, in order to maintain such variations, it will need to be periodically regenerated from seeds. Unfortunately, this was the only such seedling to appear in this batch of seedlings, so the only plant with which it could be crossed was a typical orange flowered plant from the same seed batch. Fingers crossed. Hopefully this proves to be a heritable trait and the next batch of seedlings will yield many more of these beautiful variants.