party, parti, parti--

Party or party means a gala or fete; a social gathering or an occasion for celebration--
We are having a party on Saturday. Will you come?
They are giving a party in honor of their parents' anniversary.

Party or party may also mean to take part in a celebration--
Last day of classes! Let's party until dawn!
All he wanted to do was party, so he flunked out of school.

Party or party also means a group with political opinions in common; a  faction--
He was a member of the conservative party, so he didn't vote for the tax reform bill.
His party has a majority of the house, so the measure is sure to pass.

Party may also mean one of the sides in a legal dispute--
"The party of the first part, also known as the plaintiff..."

Party may also mean a small group of persons assembled for a particular purpose--
They have been missing for hours; let's send out a scouting party.

Parti or parti means the basic scheme in an architectural design--
We'll show the client the parti, to see if they approve the design.

Parti-- or parti-- is an old-fashioned prefix ( added to the beginning of a word ), meaning varied or multi--
His parti-colored suit made him look something like a jester.
Everyone wore bright shirts and parti-colored hats, in honor of the holiday.

Now that you know that, you can say--
"Everyone wore parti-colored gowns, to make the party more festive."