When there are many child windows, it's hard to tell which window is active.

A magenta frame is added around active window title bar 

System Variables:
@AWI = 0; // No Indicator
@AWI = 1; // default, solid line, outside window frame

@AWI=2;; // title bar frame
@AWI=3; // title bar top line

and add 4 to use thin line 
and add 8 to use dashed line

For example:
@AWI=9; // thick dashed line, window frame

@AWC is for indicator color as an RGB integer.

For example:

@AWC=color(255,0,0);