pictures please

I added photos above. Here is one more. As for anomalies on the tree, aside from the prior leafminer damage you can see in some leaves above, and a few handfuls of leaves with dark green veins (most others look good I think - the lighter green leaves were new growth), the only other oddity I saw was that one of my oranges has this nasty looking spot on it. It's the only orange that I can tell that has it though, at least anywhere near this size, so was thinking it was unrelated.

I don't know your tree, but fruit drop is a common occurrence, even somewhat late in the season. If you visit a commercial groves you will see a lot of fruit on the ground. You need to remove the fruit with blossom end rot shown in your photo, and discard it into the trash..

Is your orange tree in full sun? The pics appear shady or maybe it's just a cloudy day? But if a nearby tree is shading your orange tree then that may not help. Guess guessing.

It was cloudy/rainy that day, but the tree normally gets decent sun. There is a small tree overhead that gives it a little shade but I'd say 50%+ of the day's sun still reaches the tree (from 11/noon to dusk I'd say). Do you think that could be causing this?

NO

coincidence ...??

tree time is counted in decades .. i would doubt if 3 days after spraying with oil.. it caused the color change you noted ..

that said.. ive never grown citrus.. so what do i know ...

ken