Fly fishermen care about aesthetics, well at least most of them. While you could say that this is superficial, the aesthetics of fly fishing are a large part of what initially drew many of us to the sport. And with good reason. There's a great deal of beauty in the world of fly fishing. Flies are often as much pieces of artwork as they are effective fishing tools, rods and reels are exhibitions of the workmanship and creativity of those that designed or crafted them, and so on. With so much visual stimulus, there should be little surprise that many fly fishermen have a developed a high level of attention to detail. As a result, as many fly fishermen scrutinize new pieces of gear for potential addition to their arsenal of fly gear, they are scrutinized not only on their function, but their form.
Fly lines, like other gear, likely fail to escape this level of scrutiny from most anglers. That's not to say that many of us have chosen not to buy a fly line that we thought would be best for the rod we intended to pair it with or the conditions in which we intended to fish it because of its color, but it almost certainly doesn't go unnoticed and may even serve as a scale tipper when choosing between several lines. There are practical reasons to care about fly line color, too. Many anglers have definitely turned down bright orange lines if their main quarry is selective, wary trout on gin clear spring creeks. Others may jump at such a line if they spend their time fishing in situations where fly line visibility comes at a premium.