I'm running 10.10.4 here (just upgraded from 10.9) and I notice in apple mail anyway, there is a partial transparency going on with the mailbox list on the left. I was seeing a weird orange tinge in the mailbox,and moved the window and noticed I had a window below it with an orange back fill. It's only showing on the mailbox list on the left (and the activity panel below which I have showing)
Like? No like? I don't care for it.
I work for the Department of Redundancy Department