I don't know how much fish are spooked by line color, but I can tell you that
some line colors are very hard to see while casting. I had a Cortland line that
was olive drab, and that stuff become invisible against a background of green
leaves. I really couldn't see it at all. I left it on a 4wt reel that I sold....
Cortland's 444 peach-colored line has been a standard for years, and I don't
see too many other peach objects floating naturally on streams, lakes, or
rivers, but the stuff catches fish. The only grey line I've cast was SA's Sharkskin, but that was against a clear blue sky. It contrasted with the sky,
and was visible, but a background of trees and leaves might have made it
difficult to see.
Since you say you're new, watching your line while casting is very important.
If the line is invisible.....
Cortland's 444 line is around $45, and could be a nice compromise between
flaming orange and stealth grey. It's also a fine line, and works very well with
a 5wt Avid.