Silver,"Color doesn't matter much" EXCEPT when it does!
Here's the deal. Color does matter in some situations. I am really amazed that folks that have not fished in certain situations will make blanket situations about something that they have not experienced. I have not been to New Zealand, but I have talked to Gary Borger about it and he and Jason have been there several times. Jason spent 6 moths there.
Both Gary and New Zealand fly fishing outfitters say bright fly lines spook fish over there. So if you spend $$$ to fly fish over large trout in New Zealand, would you use a bright orange fly line or dye your fly line? Of course not. The difference between not believing and believing is that those who believe color does not matter have not yet experienced a situation where color matter a lot.
I suspect that in a group as large as the members of the NAFFF, there are some of use who have seen trout move away from bright colored indicators like the day glow yellow or orange Thingamabobbers. I also have seen trout try to eat orange strike indicators during or after a Salmon fly hatch. So color can both deter or attract trout.
How about clothing color? Do those who believe fly line color does not matter also believe clothing color does not matter? Probably not. Most of us have fished enough that we KNOW clothing color does matter in how many trout we spook. So why the disconnect or lack of consistency in our beliefs?
I think it is because it matters little to us whether we wear bright or dull colors when we fish but it does matter whether the fly line is easier or harder for us to see. Bright lines make fishing easier. So if we use bright fly lines, cognitive dissonance comes into play. There is the psychological pull to believe that in this case bright fly lines do not matter.
If you are logically consistent, you will either come to the conclusion that yes, bright fly lines spook some of the fish; BUT the ability to better see the line allows you to catch more fish than you lose. OR your will come to the conclusion that bright fly lines lose you more fish than the extra ability to see the lines allow you to catch, and you will change the color of your fly lines. While making that decision, realize that it is not only about the numbers of fish. The reality is that the spookier fish tend to be the larger fish, and the fish you spook with your line color could have been the fish of your trip. That is the logically consistent position. The belief that bright fly lines do not spook some fish is simply wrong in my opinion.
You decide whether I am correct in my reasoning or whether I am wrong.
I'm not smart enough to say whether your reasoning is correct or not. But, I am smart enough to err on the side of caution. I wear drab colored clothing and use drab colored fly lines. I fish small to medium size rivers and my eyesight is still good enough that I can follow my fly line, if not always the size 26 fly on the other end of it. It is the way I was taught as a kid and it just makes sense to me.
The current issue of Colorado Outdoors has a good article on fish vision.