by glookose
the background color behind the picture on each of the original six cards indicates the color that race is supposed to play - such as green background behind the art for the Planta .... It does make it much easier to remember who is who in the middle of a six player game if you stick with the intended colors and everybody gets used to those colors.You can play how you want but if it wasn't intended for certain aliens to play certain colors then why would they bother making the backgrounds match the colors like that?
It also makes set up easier and it makes elimination of a particular alien race easier.
It just makes sense.