It was a very big deal when S&W started installing "Red Ramp"/White Outline sights. The sight picture was much easier and quicker to align than the standard black on black sights. It was very common for gun owners to put a small white dot on the front sight, since that's the sight you need to focus on.
With the advent of different styles and materials of sights, it's now possible to have both glowing night sights and bright FO sights at the same time. The colors have become an individual choice. There's no optimal color or combination that's perfect for everyone.
You should get the combination of colors based on which ones tend to attract your eye. If red gets your focus first, make that the front sight color. If white, orange or green catches your eye first, use that one. Make the rear sight more visible than just plain black but less prominent than the front.
Sometimes when you have red front and green rear sights, your brain has to stop and think about which color is which. Making the sights on all your guns the same color combo reduces variations, and thus the delay in recognition.
So, obviously the benefits of contrasting colors on sights has been around for many decades. I had these exact sights on my S&W 586 in 1985.
