In the interests of full disclosure, we'll start by saying that the Premier League appear to have broken one of their own rules by allowing Norwich have the three kits above. The PL handbook states that at least one of a club's change kits should be different enough from the home kit that it could be worn against it and it's arguable that Norwich don't achieve this. Then again, this was allowed in 2013, so it's not as if they're always on top of things kit-wise.
While we accept that another colour might be needed if Norwich were in Europe and played Nantes, we believe that what they have is sufficient. Let's look at the instances where they would need to change (as opposed to those games where alternative kits are worn simply to get people to buy them):
The only other side in the Premier League to feature yellow in any prominent fashion are Watford, whom Norwich visit on December 5. The Hornets have a lot of black this season but Norwich's green away ensures no confusion (left) - the green home shorts can be used to make things even more clear-cut (right).
The green strip will suffice against any of the other teams in the league with a yellowish tint, but of course the home is a halved effort this year so Norwich clash with teams in green too.
Realistically, the only two examples of that are League 2 sides Plymouth Argyle and Yeovil Town. Plymouth are already out of the FA Cup, but we had these kits drawn anyway. The third shirt up against Plymouth's home is fine, in our view (left). There is a shorts clash, but that's easily alleviated if the away shorts are used (right).
Yeovil are still in the cup and might be third-round opponents, but they have no black on their kit and so the third kit has enough differentiation, given two-thirds ratio of yellow/gold to green (below and below left). And if you don't agree with us, take it up with the Football League, who allowed Yeovil to register a yellow and green away kit, which will presumably be worn away to Plymouth on Boxing Day (below right).