Unusual fall color????????????

It's neither a pest nor a disease (in the sense of an organism causes it) but here is an example of an unusual case of chlorosis AND fall color in an American red maple seedling that just showed up one day in one of my grow boxes.

At least I THINK it is chlorosis, but the nearby green leaves show no sign of it. (I wonder if it is patentable?)

Very similar to my trident autumn colour this year. It's been a weird season here. Early warm spring, cold summer, very warm early autumn. Everything seems confused!

Magnesium deficiency. Shows up in oldest leaves first as magnesium is highly mobile. Also brings on early autumn colors and early leaf drop.

Paul