To cover every decoying situation, a cammo net must be long enough to make a comfortable four sided hide, i.e. six metres wide and high enough to conceal you when sitting behind it, generally about 1.5 metres.
I think we all make an effort to blend the colour of netting with the background where we are shooting, but I am not convinced it makes that much difference.
Keeping still as pigeons approach, and general hide discipline is far more important.
But at least making the hide as invisible as possible removes any nagging doubt that it may be putting birds off.