When I have a lot of apps open, I lose track of which window is which.
These days everything has the same dark UI — the terminal, the editor, the chat
app all look alike at a glance. I kept opening Mission Control just to find the
window I wanted, and it quietly added up.
So I gave each app its own color. Pick a color per app, outline that app's
windows in it, and you can recognize them at a glance — blue is this, red is
that.
https://github.com/crazyathlete220-stack/window-border
What it does
It's a small menu-bar app. Under the hood it just asks CGWindowList for the
on-screen windows — their position and which app owns them — and draws a colored
stroke along each window's frame. Because it only reads geometry (not pixels), it
needs no screen-recording permission. The outlines are transparent and
click-through, so they never get in your way.
Colors are auto-assigned per app, but you can pin them in
~/.config/window-border/colors.json if you want "Safari is always blue."
The fiddly parts
It looks trivial, but it took a few tries to behave.
First, the outline sat slightly off from the window. macOS was "helpfully"
shifting my borderless overlay to keep it on screen; turning that off fixed it.
Then, dragging a window fast made the outline disappear behind it. The outline is
a separate window, so when the dragged window jumps to the front it covers the
outline. The fix is to lift the outline back on top whenever something moves.
Finally, the active window's outline kept hiding — every click or keystroke
raises that window above its outline. So the frontmost window's outline gets
re-lifted every frame.
Doing all of that every frame would be heavy, so it only re-stacks when something
moves (plus the frontmost window). When the screen is still, it does nothing.
The limit
The outline chases the window, so a very fast flick leaves a one-frame trail.
That can't go to zero — you can't physically attach an overlay to another app's
window.
No private APIs, MIT licensed. Color-coding turned out to be more comfortable
than I expected. If you also keep asking "wait, which window was that," here you
go.