Colress is an antagonist, but he isn't exactly evil -- not like Ghetsis. He works for Team Plasma, but only does so to "draw out the true strength of Pokemon". He battles the player several times but does not do so with any intention of stopping them. He gives access to Ghetsis' chambers after beaten, wanting to see if the player can defeat him. He's not the new professor, and Juniper remains in Black 2 and White 2.
In short, he's an antagonist, but he's more interested in his own motives, rather than blocking the player from progressing.
