You'll mention on the 60th birthday party invitations that dress for the event is black and white cocktail attire. But what exactly does that mean? Well, much of how you (and your guests) dress will be decided based on the invitation.
In general, it's dressy but not exactly formal. You can wear all one color or mix them up. That's the fun in it. There are only two colors, but they are far from boring.
Women The little black dress was made for this party, but any white or two-color frock will do. Just make it no longer than knee-length and not office appropriate.
Men A simple black suit is classic and refined. To jazz it up a bit, lose the coat and wear a tie with patterns (like dots and houndstooth).