I remember reading some time ago that there was research done on goalkeeper kits which found that gks who wore bright/fluorescent kits appeared larger and so more impenetrable to an oncoming forward. And last season Manchester United (I think) changed the colour of the banners surrounding the Old Trafford pitch away from red because it was felt that the players were not seeing each other well with red shirts against a red backdrop.
Personally, I am absolutely convinced that players wearing bright/contrasting kits will be more visible to team-mates, especially in peripheral vision. So a player on the ball might be more aware of the movement of a team-mate who might otherwise be less visible to them. I suppose that this would also be offset to some extent by increased visibility to opposition players also but I am inclined to think that the positive effect would exceed the negative one - there's not really much scope for camouflage/stealth attacks in football whereas instant awareness of the position/movement of teammates could be a big advantage.
In Argyles case I don't think it shirts v pitch colour that is the issue (shirt green is significantly different from/darker than grass green) but, rather, darkness/dullness of shirts against the generally dark/dull colours surrounding the pitch.
I wonder if anyone has asked the players about this. It might not be a huge difference but if there is any negative impact of the shirt colour on the playing side of things then it ought to be modified.