I'm focussing my efforts this year on catching some nice Ontario Brown trout. These fish spook very easily, and are the focus of a lot of fishing pressure - the most successful fishermen must be as stealth as possible. Currently there is an awesome sale on some Rio fly line at a local shop - Rio Grand for $10.88 - but it is bright orange.
Will this color spook trout. I know when I go trout fishing, I keep as quite as can be, and wear very earthy colored clothes in an attempt to stay as stealth as possible. My worry is flinging bright orange line may not help my quest for browns.
I have always stayed away from brightly colored fly lines so don't have any first hand experience. But, if you are trying to be stealthy I would not be using a bright colored line. If you false cast over the fish, or within its window of view I would suspect that you could put wary fish down. That could be said about most fly lines. The trick is to false cast away from the target and then deliver the fly to the target by shifting direction.
For 10 bucks you could try changing the color with colored markers. The best you could hope for would be green or brown. Why not buy the line and use it to practice with. Save you other lines for fishing.
My Selective Trout is Chartreuse and I have had the ORANGE line before. First off, it should be the leader the fish MIGHT see not the line. Gin clear water I will even use a 12' leader. and there no false casting just one roll in front and let it drift.
I think too much is put into Clothing, Rod/Reel, Line color. I usually wear a BRIGHT yellow hat and either PINK or Purple shirt and my reels are Titanium colored along with black, green, etc. My indicators are usually bright!
Just all in the delivery to me, just my opinion.
I'd go with Joni on this one. A larger leader might be a key. I've fishing a few shallow ponds that were loaded with trout. Thing was this water was artesin flow, this water was so clear you could see the trout no matter where they were. At times I had to stand several feet away from the bank or even down in low areas. I had much better luck with a small mepps size 0 then I did with flies on this place. The trout that were in here were all small rainbows, but I seen many a time a fish come look at a fly (wet, dry, streamers) only to turn a way or spook way from it. I use a light peach, almost skin color fly line. I've tried adding a bit of other color to it trying to make it camo color and that didnt work so well. The best that I've done has been with a longer leader (adding a few feet of clear color mono before the tippit) and fishing mornings or later in the day when sun light isnt as strong. The less light seamed to help with picky fish. Now this was pond fish not river run browns. Part of my success was the fact these ponds were heavily populated and compitition was high. As a roll fish looking up have a harder time seeing bright colored objects, looking down black is hard to see. Trout seem to be an exception and seam to see everything at times.
I agree that the line is generally the least of the variables, and a longer leader will help. That said, line color will effect visibility in different environments. If looking up at the line from the fishes perspective and the background is primarily bright (wide open sky), colors with higher reflective values are less visible. If the background is a canopy of trees or bottom, darker lines are less visible. My still water lines are light in color, but on streams I don't worry as much as the fish aren't as deep so their perspective is generally limited to the leader anyway. My $.02
I adhere to the same philosophy as you do, and prefer drab colored lines such as willow or Tan.
I've been taught that yes we are fishing, but we are "hunting and stalking" also, A quiet, slow approach will often times get you much closer to your fish.
And by trying to be as inconspicuous as possible and blending into our natural surroundings as much as we can 'imho' can only help us to be successful.
Now on the other hand, and Joni alluded to this, "presentation" is equally important(more so on some of the heavier fished rivers). Changing the angle of approach and lengthening of the leader and/or Tippet, sometimes to an overall length of as much as 16'-18' on the Henry's Fork is common.
With that said, Orange is not a color I prefer personally, but the price on that flyline is very good. I would go pick up 2-3 of em and worry about the color later.
Frank mentioned using a marker on the line, even if you only colored up the first 15'-20' you would probably be fine.
I personally don't think the color of the line would be as much of a problem as the type of line. The Rio Grand is a very heavy front tapered line that is designed to be used with fast action fly rods. My personal experience with the Rio Grand line has been great for nymph fishing but it does not present a small dry fly well. All lines will cast the same shadow, no matter what the color and how light they land on the water can also be a bit of a factor. I would not hesitate on the line color but I would be more concerned about the delicacy of how you can land that particular line on the water.