Originally Posted by g_conway

TFO stands for Tritium Fiber Optic.
It has both Tritium for night use, and fiber optic for daylight / lowlight situation. Best of all worlds as far as I am concerned.

As to color...
Everyone has different needs and preferances.
As others have stated, GREEN is the brightest and the human eye picks it up best. That said, I use GREEN on the front and YELLOW on the rear. The yellows are just SLIGHTLY dimmer than the green but provide an obviuos differance that allows me a very quick way to pick up and center the front sight in dark / low light situations. Just my personal preferance.