It's been my experience that animation looks to color and exaggeration as keys to creating a dynamic product. Just like most superhero costumes look crappy if exactly rendered into live action, teams of people colored exactly alike tend to make animation look dull.
The producers of RGB were unable to use the actor likenesses. That's a fact. So they went for caricatures that didn't even look much like the actors, giving Ray and Egon different hair colors in the interest of a far more dynamic product visually.
They produced a trailer where the Ghostbusters wore the exact same tannish flight suits…and somewhere along the line somebody probably decided that the color pallett was still too limited and dull for the requirements of animation at the time, thus the more colorful flight suits.
Ghostbusters is far from the only property to undergo color makeovers for animation. Take the
Teenage Mutant Ninja Turtles for example: in the original Mirage comics, on the covers and the occassional rare color issue, all of the Turtles wear red masks. When it came time to put the Turtles on TV, the animators took the bunch (who look far more alike than the Ghostbusters ever would) and came up with the idea of different colored masks to help differentiate them. Raphael, like Ray Stantz, got to keep his original color…everyone else got a makeover.
The Turtle's color infusion has carried over into every version ever since…Mirage is pretty much the only ones who color all four in red masks. The live action movies and the newer cartoon, while keeping closer to the art stylings of the comics, still use the different masks. They've even given the Turtles slightly different shades of skin tone. I'm sure there are purists out there who whine about the TMNT's not all wearing red like in the original, but I haven't heard it.
Suffice it to say that there's still a
minority of us out there who think the animated likenesses are more interesting and dynamic, and don't get insistant that the Ghostbusters must be four guys in tan who look like Murray, Aykroyd, Ramis, and Hudson.