I'm sure they meant well, but lately Google+ has been "enhancing" the black-and-white photos that I have been posting with a brown "sepia tone". Normally, especially on color photos, I like the automatic enhancements that Google+ makes to the photos, but turning a black-and-white photo into a sepia tone photo is going too far. Luckily, you can remove it.
Click on the photo and hover over it until you see the word "enhanced", then click revert. The brown color goes away. I just posted some black-and-white photos from the 1960s, and they really should be black-and-white. Sepia tone is for photos from the 1800s. And if I want sepia tone, I will put it in the photo myself.
I don't know why they do this kind'a stuff, but they do.