Does the color of your line make any difference?
I mostly fish streams, so is there a certain color of line that I should be using?

i think general conseneus is that any line viewed from a fishs viewpoint is going to be black (ie like a shadow ) yet you will get some (insert self) who will say that a nice grey or olive instead of a floro color is a good thing . in the other camp some will say its better to be able to see your line so as to know when to mend it . for a beginner id say stick with a high vis line till you get mending down

Personally, if I have the opportunity to choose, I use the darker leader for canopy streams and clear for meadow or open streams.
Whatever would melt with the background above the water best.
Thats a dry fly tactic ofcourse.

Motley,
If you're a new FFer, I wouldn't worry much about line color. Bright colored lines are easier to see and this will help you with casting.

I don't think line color matters much if you make a decent presentation because the fish should see the fly before it sees the line. That said, an olive or grey line is used by many because its a bit more stealthy than a bright colored line. I think Quillfly is right, all lines probably look dark or black to the fish anyway. I've caught lots of trout both kinds of lines. Use the line you have and work on the drag free drift.

Well, the question revolves around visibility for the angler vs. the fact that it may spook fish.

Frankly, I don't think it really matters on either end. I can see drab colored lines just fine. And I doubt brighter lines spook fish anymore than drab ones do, it'd at least be very rare that it makes a difference.

Given the choice, I choose drab colors. Olive and the like. But it's less important than the quality of the line. I look at reviews and taper, durability, etc. before worrying about color.

I have used every color line manufactured and have had the same success with all of them. If you line the fish it could be transparent and you'll spook them. I really think it is all about visibility to the angler. That's just my opinion but I honestly don't look at the color of line when I buy it. I need a 5 weight, I see a decent make on sale and I buy it. Could be purple and it doesn't matter to me. Now i generally use a 12 foot or longer leader so if you go shorter maybe it then makes a difference.

IMO color makes NO difference. The trout should never see the fly line to begin with. If they do it does not matter what color it is they will spook.