An XS Big Dot sight is an option for the sight-impaired. The tritium vial surrounded by a wide white circle gun results in a front sight in daylight that is probably about 9 times the area of just the vial, which is likely the size of a normal front sight dot. It would be hard not to notice such a big front sight.
The tritium would be useful in dim light, and the human eye is most sensitive to the color green -- yellowish green in bright light, bluish green in the dark. Thus, green tritium makes sense. In the dark one needs to illuminate the target to see it; thus, a flashlight is essential. I don't like the idea of attaching a light to my pistol -- I don't have a rail, I don't need the additional bulk when I carry, I don't want to give an intruder a bright target to shoot at, and there are many more times that I need to draw a flashlight than I need to draw a gun, and I don't need a pistol barrel attached to my flashlight when I use it in a non-threat situation.
A laser sight would definitely help, but it again gives a bad guy a target and adds bulk.