In dirty water, i don’t think it much matters. I clear water i think it might help. The last couple lines i have bought have been olive/dun colored, i figure it can’t hurt, especially if you don’t have trouble seeing or need the help to see the line. One additional note, we fish glow in the dark lines during the Hex hatch, and also when skating mouse flies at night, and it doesn’t seem to bother them at all, and we use at the longest maybe a 5′ – 10 lb leader for that stuff.
I really want to do some snorkeling or scuba diving in my local river this summer, and i have a underwater Nikonos V camera from the scuba days, if i can, i’ll get someone to cast a couple lines over me and try to get some pics.