Could possibly be Boxelder Acer negundo 'Sensation', a found selection I rather very much like and wish to plant one for myself, where as I've never been a fan of Boxelders in the first place, so that says a lot of the desirability of 'Sensation'!!

@FrozeBudd_z3/4 I actually came across Sensation in my search a few years ago, but I have never seen a green leaf on the one in Estes. But, it could just be that I was never there when green leaves were present@

If by "permanent fall color" you mean trees that have foliage color other than green, there are many!

Asian maples probably lead the pack. Japanese maples and their close cousins come in just about every leaf color you can imagine - maroon, red, orange, coral, peach, yellows and golds, pink to nearly white and various combinations of them all. And most offer a second blast of a different fall color as well.

Redbuds - Cercis canadensis - have both purple-red and gold leafed cultivars and a new introduction, 'Eternal Flame', that combines them both.

Various trees have yellow or gold foliage - Gleditsia 'Sunburst', Robinia 'Frisia, Catalpa 'Aurea', etc.

Lots of purple leafed trees as well - plums, cherries, crabapples, beech, elderberry, smoke tree, 'Summer Chocolate' mimosa.

add location to every post .. not all trees grow everywhere ..

what about a copper beech .. it has the coloration you speak of ...

https://duckduckgo.com/?t=ffab&q=copper+beech&iax=images&ia=images

and to be clear.. they are rarely the color you see in these pix ....

and why not in winter.. are you presuming deciduous???

ken