I always thought lilies do not revert but I am seeing in a Facebook group where someone is saying that yes they do revert. I need some expert info here to pass along. Revert or not?

Well, you are correct: THEY DO NOT REVERT NOR CAN THEY REVERT. I know you'd like to, but for me, I wouldn't bother wasting my time passing along expert information to some make believe expert on Facebook who would make such an ignorant claim. More often than not, they won't accept your explanation as fact anyway. To borrow a thought from a fellow forum member on here: 'There are those that want to learn---and those that never will'. Just sit back and chuckle at what they say, then smile---because you know better.

Thanks, Lorn. I will try to do that but oh I so want to tell them .

I'd say something so as to benefit the rest of the group that may fall for the bad info being passed along by the knucklehead.

Lorn is right.
Reversions are mutations back to whatever the original form was. Since lily cultivars are not produced through mutation from an original form, lilies cannot revert because there is nothing to revert back to.

Original form → mutates → produces mutation → reverts → produces Original form

Many hosta cultivars are great examples of mutations (not reversions), since many new cultivars come from a mother plant that grows (mutates) an offset different from the rest of the plant. A variegated blue and yellow leaf offset from a normally blue leaf mother, for example.

Now if that blue and yellow offset then grows on, and part or all becomes all blue again, but a different blue from the mother, that would be another mutation.

But, if that blue and yellow offset then grows on and becomes the same blue again, that would be a reversion.

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All this said, there is only one unbroken rule in the natural world: There are no unbroken rules. Nature continually evolves, but at such a slow pace that we seldom realize. In the unnatural world, lily mutations have been exploited in through forced chromosome doubling (i.e. tetraploids). Though I've never heard of any spontaneous changes back to a diploid form. If there is such a case, that would be a reversion. I doubt such a facebook claimant would even understand the concept, so the idea is inconsequential to the discussion.

I know in the peony they can revert back to the original species..... that happened to a number of plants at a number of houses in this area last winter when the weather was so brutal. the way I was told that with the hybrid part killed off due to the winter...the species shows up instead. I know have a number of species type peony. The lily breeder that I bought a number of lilies from tried to explain this to me but it was way over my head to be honest. But the nice vivid peony that were once a very pretty shade of wine almost are now a light pink with fluffy petals and white inside and a yellow stamen. They also produce seed pods.

I have not heard of it in lilies before

I also have a red maple that is going back to a green maple instead............
Had this happen in a honeysuckle that bloomed orange for years and now this year and last is light pink with white centers instead..........

They say a brutal winter does this to plants............or some type of plants.........anyhow........... all I know is the hybrids are now all species instead...........and in relation to the flower on the honeysuckle it was packed full of more blooms and the other year the orange was sparse..... and on the peony the flowers are much bigger but fewer of them. Both the peony and the honeysuckle are well over 80 years old here.....and this is the first time this has happened. This year they all bloomed with the species again since apparently they can not go back to the hybrid........so I was told.

Grafted plants are affected by many additional factors regarding reversion. Lilies, because they are not grafted, have none of these concerns.

If not reverting can you explain why most of my asiatic and oriental lillies which used to be many different colours are now a light cream yellow?

Can you provide photos? The most likely explanation (if they're all in the one bed) is that one cultivar has taken over.

I had three different oriental lilies: all white, pure yellow, and white with pink. Now all of them are a pale yellow. Maybe it technically is not reverting, but they for sure did change colors!

to the forum, @simwest! It sounds like the yellow cultivar may have taken over. Were these bulbs all mixed together in the same bed, or separated by colour?