Just a silly question. I read through the rules and couldn't find out why you would need 2 different colored die. Are there situations where you need to roll against an event?
Probably just an aesthetic choice on the part of the publishers, I suppose. Opening a box and seeing two different coloured dice, I have a vague feeling, might have a nicer feel to it than seeing two of the same colour? Certainly, I haven't been able to think of an occasion where, in game terms, it's necessary to have them in different colours.