We started with white, but it's hard to read in Pronterra streets and it's the same color as normal chat white. We switched to yellow, but then it's the same as private message and GM annoucements.
heRO been through both colors and found both of them to be inadequate ^_^; we had many votes on them too in the whining thread from the past.
You can just type @main in the whisper box (the bottom left hand corner) so you don't have to type it every single time. Just leave @main in there and you can always talk on it without repeating @main in the beginning of every message.
EDIT: I like snow bunnies too