I guess we associate autumn color today with senescence of leaves asociated with ANGIOSPERMS or some conifers like Larix and Metasequoias

But leaf senescence is probably older than THAN the existence of both angios and gymnos

TEMPERATE palaeoclimates date back to several million years an temeparate forests could have existed in Carboniferous

But THE STRONGEST EVIDENCE of leaf senescence and color could've been driven by herbivory by insects and as a response to cooling temperatures

We find ample evidence of LEAF SENESCENCE in WHAT WOULD NOW CORRESPOND TO  temperate deciduous FORESTS in GONDWANA

Forests of GLOSSOPTERIDS with autumnal clumps of leaves have been found particularly in India

You could then see the phenomenon of senescence IN AN ANTARCTIC FOREST WHICH PLAUSIBLY CHANGED COLORS A PHENOMENON which we today near exclusively reserve for angiosperms 

But GLOSSOPTERIDS couldve been changing color in the permian too

Similarly THE PERMIAN ENDS with the extinction of GLOSSOPTERIDS but the Triassic bings in conifers and related gymnosperms like GINGKO RELATIVES the relative of which is GINGKO BILOBA that can change color even to this day

The Jurassic see further evolution especially in Middle Jurassic which had cooler temperatures and saw the ecpansion of temperate froests AND THE GENUS GINGKO though some GYMNOSPERMS couldve changed color

Creaceous sees the expansion of angiosperms and by the late cretaceous we had already Magnolias Platanus like plants

But the major expansion came in Palaeogene when Maples beeches katsuras appeare coloring the landscape as we know today

But since majority of fossils never show up in record senescence existed and AUTUMN COLOR could very well date before the first dinosaur

Autumn color in ancient history