I only have one gun that came factory equipped with fiber optic sights,colored are the reverse,green in the front sight,red in the rear.
They show up very well in all light situations,I was surprised at how well. The only problem that seems to plague most F O sights is the front sight tube fell out while shooting,I would guess from recoil.
I happened to see the tube on the bench top and put it away,when I got home I reinstalled it with super glue and touched the rear tubes while I was at it.
That was over a year ago and no more shot out or lost color tubes,just a fore warning.