Have PTs on two of my Kahrs. I like the different color rear sight (I chose amber) for my wife, as they give her a better chance of correct alignment if SHTF in the dark. The rear elements are significantly dimmer than the uncolored (green) front sight, though (actually, this may be an advantage as the eye is drawn more to the front sight).
My Glock 27 (main carry gun) came with factory Meprolights - all green - and I like these just fine too. In all honesty, my presentation from the holster is so ingrained that I don't worry about sight alignment at all. The all-green sights seem to be a little brighter, which I like.
So there you have it... if you get a lot of stick time drawing from the holster (i.e. IPSC shooting), then use the brightest same-color sights you can find. If you are only an infrequent or cassual pistol shooter, then the different color units from PT are worth serious consideration.