I recall reading an article a couple of years ago in Adventure Cycling. The gist of the article was that while fluorescent colors are, indeed very visible from long distances, they tend to create target fixation. You know, that phenomenon wherein you look at the obstacle you want to avoid and wind up hitting it because you're looking at it, instead of the path to avoid it (not that I've ever done this ).

This very experienced rider's conclusion was that a merely bright color would be a better choice. Just enough to catch the eye and register in the driver's mind that someone is there, then their attention can then go back to their intended direction of travel.