Active windows are almost always indicated in some graphical way, but not that distinct that you would be able to tell the active window in a split second. And that is how fast you would like to, wouldn't you?
Here is a AutoHotKey script for you. Activate it by ctrl+super+space and toggle with super+alt+space.
; This script puts a red border on the current window.
; Nice to have something clearly indicating what is active.
; Author: @danielgasinski
; Source of inspiration http://blog.sveri.de/2010/01/27/script-to-draw-a-border-around-an-active-window-with-autohotkey/
Toggle:=0
^#space::
Loop
{
if(Toggle != 1)
{
b = 6 ; border
full_width = 1936 ; w value from WinGetPos, lite more than screen width
WinGetPos, x, y, w, h, A
if(w >= full_width)
{
b:=12 ; We make the border thicker when in full screen, otherwise it may not be visible
}
width:=w-b
height:=h-b
Gui, -Caption +Lastfound +AlwaysOnTop +Toolwindow
Gui, Color, FF0000
WinSet, Region, %b%-%b% %b%-%height% %width%-%height% %width%-%b% %b%-%b% 0-0 %w%-0 %w%-%h% 0-%h% 0-0
Gui, Show, w%w% h%h% x%x% y%y% NoActivate,
}
Sleep, 50 ; Chance/time to interupt
}
return
; Toggle on of alt+win+space
!#space::
Toggle := Toggle<1 ? 1 : 0
Gui, Show, w0 h0 x0 y0 NoActivate,
return
Example of how the script works.
Nota bene: ignore the semicolons on row 18 and 39. It is something fishy with the AutoHotKey highlight script making them appear in the post. Sorry.


