I'm guessing your talking about fiber optics on a sight??
My favorite is green, it shows up easy without starbursting on a bright day.
Red is a close second, but it'll do a little starbursting in the sun.
Yellow isn't bad but for me it disapppears first at dusk.
Forget blue it dissarrears in the sun
I use green for 20, red for 30, back to green for 40, red for 50, and green for 60.(just for Barry)
Those are the two that show up best for me. You'll just have to try and few and see what works best for you.