I want to know more

Me too. I took this photo about two years ago I think because I was weirded out by it lol. All I know is that it’s a type of gum tree/eucalyptus. Location: Sydney, Australia. I couldn’t tell you what specific variety of gum tree this is unfortunately. I have a lemon-scented gum tree in my front yard but it only turns a darker blueish grey when it rains - not super colourful like this. All the other trees of the same variety also seemed to do this that day. Was really weird but cool. Some of the other gum trees were turning bright red (I think they were Angophora Costata) too.

Very otherworldly, I hope a mycologist/environmental scientist can help explain! :)

1, 2, Freddy’s coming for you….

I hope so too! The only possible explanation I can come up with is that the tree had recently shed its bark and the bark underneath was still soft and greenish. Gum trees do this weird thing where they shed off all their bark once a year and can change colour quite significantly when they do. Doesn’t explain why the rain had such an impact though.

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Did some research and found this explanation for you:
"Two reasons are possible.
The first is that there is photosynthetic tissue in the bark. It is hidden by bark pigments until the bark gets wet.
The second is algae and/or mosses that colonize the bark. They go dormant when there is no rain, but quickly inflate and become active when the bark is wet.
In any event, greening of trunks is not universal. The bark of some trees inhibits colonization by algae or mosses, and the bark can be too thick to support living photosynthetic cells. It is normally trees with thin bark that have photosynthetic cells near the surface."

Now explain to me this phenomenon if possible that I experienced years ago.

In the dead of bone chilling winter past Christmas I saw dim little green and red twinkling lights all over multiple trees in my neighbors back yard.

I thought a couple possibilities.

Some sort of glow worms or fungus but they apparently just wouldn't survive in below freezing temperatures as far as I know.

The other was lights or a light projector. However, I did not see any wires at all and I looked closely and the projector doesn't make sense as the lights were on all sides of the tree that I could see. A projector can only project onto at most half of the surface of a standard object.

Awesome! Thanks so much for that :) is this specific to eucalyptus species or do other genus do this as well?

My neighbor has a tiny laser projector that does this onto the trees behind my house. It's quite cool.