While I must admit that Flying is scooped under the Colorless banner, for the most part, Colorless is where Normal-type Pokémon go. As best I can recall, the only three types effected by Normal W/R in the game are Dragons (weak), Ghosts (immune), and Rock (severely ineffective). Granted, I haven't played the game in a long time, but still.
It would just be sort of weird to have a Butterfree being weak to a Rattata. I'm actually surprised we haven't seen more Fighting-Rock Pokémon resistant to Colorless in the TCG.