I'm on Lubuntu -- Ubuntu 16.10 LXDE desktop. I have refused to upgrade to the latest version (Ubuntu 17.x) because I haven't quite figured this one out, yet. Perhaps that is why I can only download Opera 45.x? (I just checked again, today.)

I had never used the dark theme. So I enabled it and tried this again. The Menu/tab bar still changes color upon each reload of Opera. It started off with the beige color (same as my last screenshot), went to green, stayed green the second time, then went to the mauve-pink. I stopped before it could go to hot pink, which is the most annoying. Then I unchecked the "Enable dark theme" box, because I do prefer the lighter theme.

I had used one of the basic wallpapers that (I think) came with Opera. I can't seem to find a way to have no wallpaper, now. There is a white wallpaper in the choices, but when I use it there's no effect on this hot pink menu/tab bar. In fact, none of the wallpapers I have make any changes to the issue.

Thanks for looking!

I took a series of screenshots one right after another, closing and re-opening my browser between each. (I thought that they were taken a minute or two apart, but I discovered that they were just several seconds apart.)

A couple of days ago I updated to Opera 45.0.2552.635, and as soon as I opened Opera I discovered that the Menu/tab bar was hot pink in color. I really DO NOT like pink! Since then, every time I open Opera, the bar is a different color. Right now it's a subdued mauve-pink. Once or twice it's been a pleasant green color. But mostly it stays in the pink range, from hot, almost neon, pink, to fuchsia, to mauve and some ranges in between. Why is it doing this and how can I change it? I can't remember what it looked like before the upgrade, but it was unubtrusive, and I'd prefer it be that way. This pink at the top of my browser is disconcerting!

I am on Lubuntu 16.10 (x86; LXDE)