Okay, I know you need both red and green versions of the game to complete it, but Satoshi Tajiri first picked green as a color before picking red (actually his staff picked Red, he hates the color because it's the color of blood). So I guess this makes Pokemon Green the version that's more in line with Satoshi Tajiri's vision, at least in terms of color (since he hates red).
And so, that would mean that the game assumes you pick Bulbasaur as your starting Pokemon (since he's the only starter Pokemon who's green, the first Pokemon who appears in the intro title screen of Green, and Venusaur is the mascot of the Green version). In addition, I think we could say that the game assumes that we pick Green as the name of the player character and Red as the name of the player's rival, because Green is not a name in real life but it's in Pokemon Green as a default due to game's name. And taking this into consideration, it would be natural to call the player's rival Red, since Pokemon Red is the counterpart of Pokemon Green. And the player character's name was not officially named Red until the games that came after the original Red and Green versions.
So that's what I have to say.