Colored trigger, differently shaped.
Extended, threaded barrel, custom contrasting finish.
Custom stippling of the frame.
A set of aftermarket sights that improve on factory sights—nite guys
Custom colored magazines.
Custom mag base plates, especially if extended.
Don't do slide windows.
Remove the rail.
Round all slide & frame edges & refinish
Choose a unique custom pattern Kydex holster
Load Barnes' XPD bullets
With a colored Uplula.
Stipple the top of the slide between the sights to reduce glare.
Adjust slide stop to autoforward.
Have controls with contrasting colors to the slide.