Why is Proteus a Rusty Hive?

A few weeks ago I noticed that my Proteus hive was rusty on the top, unlike the other hives. I thought perhaps it was because I had a flower pot on top without a saucer. I removed the flower pot and wiped the top of the hive, but some of the rust stayed. The rust continues to be bright orange on the top cover.

Then I noticed the concrete pavers that I was using to lift the hive off of the deck surface had changed color from gray to rusty brownish orange. Hmmmmm.

There are three trees that my deck is built around - with circles cut in the deck floor to accommodate the tree trunks. The other two hives are near and under pine trees, but Proteus is under an oak tree. The oak sap must be causing the rusty effect.
I set up my ladder and attempted with my lopers to reach the oak branches to trim them. Well, I need a taller ladder or longer arms or a super-duper loper to reach these branches. One pitiful branch fell right at Proteus' front door before I gave up.

We're almost through spring and moving into summer. The sun hits the deck much earlier in the summer. Here in spring, the hives get touched by sunlight from early morning on but my house faces S/SE and it takes a while for the sunshine to hit the hives fully. That happens after lunch. But as we move toward summer, the sun is there earlier and may help with this rusty effect. Meanwhile, I'll just live with rusty Proteus.