Well if you are river fishing the fish should never see the fly line so it shouldn't matter at all. That said I always go for a pale green line, a lot of my fishing is in heavily bushed streams and green seems to show up less

It's not just about not being seen by the fish either, I see all sorts of wildlife when out fishing but I'm sure I'd see less if I had ten yards of fluorescent orange string whirling around my head.
Sinking lines must be dull green or brown or clear in my book, anyone remember HF's white sinking lines, they caught on well didn't they
Andy