I like a white party, I don’t know if it is still in fashion or not. Black and white is supposedly very in this season, so you could go with black and white party.
A friend of mine had a pink party and even the men made sure they showed up with some pink on.
If everyone is around 45 years old you could do an 80’s party and it would capture the teen fashion for the group. Adjust depending on the age of your peer group of course.
Is the party at your house? Or, out at another location?
Edit: this link shows invites as recent as 2012.