Actually, I heard that they ARE bringing out a third kit...
Working on the theory that the away kit will be blue (I'm not ITK, it's just a guess), then we would NEED to wear the away kit against the following...
A third kit, in...lets say, red, would be worn against teams where the white and blue kits couldn't be worn. So those would be...
Brighton and Hove Albion
And possibly Peterborough United, depending on the design of their home kit.
In the world of logic, you'd just have a red away kit. But this is the world of money-making. I think it's actually in the rules that a team has to have three kits available to wear, alongside two goalkeepers kits, in case of clashes. Ordinarily, a team would just wear their away kit from the season before. However, when a team changes kit manufacturers in the close season, that is no longer possible, so a third kit, usually not worn all that often, is released.
Alternatively, it'll be a red (or yellow, or something) away kit, so the blue third kit would only be worn in the event of cup clashes vs, say, Arsenal, or Sheffield United.
In short, there'll be five different kits up for sale this season.
I love that you spent ages doing some homework into this, like you were trying to crack the Da Vinci Code; when it's not actually a secret that there IS a third kit next season.