Three years ago, I wrote about marking the active window (update here ) so that it’s easy to pick it out from the other, inactive windows. I did that by making the mode line of the active window a distinct color instead of the slightly different shade of gray from the other windows. That’s worked out really well for me and I’ve never looked back.
Now Ray Zeitler over at Ray on Emacs takes another look at the problem and found a really nice solution. It’s a bit more in your face than mine so if you’re looking for something that makes the active window really stand out, you should take a look at his post. The TL;DR is that instead of changing the active window, he changes the background color of all the other windows.
Zeitler found his solution on a 10 year old Stack Exchange post so it’s pretty certain to work no matter what version of Emacs you’re using. The code is very simple and you can simply copy it to your init.el if you’re interested.
As I said, this solution seems a little aggressive to me so I doubt I’ll be implementing it but others may disagree. One thing for sure, it’s going to make your active window stand out. It’s a small enough change that you can try it out—say by copying it to your scratch buffer and executing it—to see if it’s something you’d like.