Hugh Hefner and Crystal Harris know they are not a conventional couple. So, why settle for a convention wedding when the pair will exchange their vows on June 18?

"The dress is not going to be white," Harris tells PEOPLE of the Romona Keveza gown she's selected for the occasion. "I love pink! So, the dress will be pink and Hef and I want the wedding to be just a lot of different colors and to just look beautiful."

Harris, 24, and Hefner, 84, are in the midst of planning, "and it's pretty great that we haven't argued about anything yet," Harris says. "Things that I feel strongly about, he's okay with, and things that he feels strongly about, I'm okay with doing things his way, so it works out."

Still, Harris admits, "It's cute having him look through catalogs for wedding cake toppers! So that has been a lot of fun and seeing it all come together."

Hefner favors strawberry cake, and so that's coming from Torrance Bakery. The flowers will be fuchsia and turquoise, matching the Swarovski crystals that will adorn the more than 300 Papeterie custom-made invitations the couple is sending out.

"Hef's friend Ray Anthony, he has a band," Harris says, "so we're going to have a big band and we're going to have all kinds of instruments and we're going to have a deejay towards the end of the evening."

In terms of the wedding party, Hefner's brother Keith, 82, will serve as his best man, with Hefner's two youngest sons, Marston and Cooper, 20, his groomsmen. Harris will have her two older sisters as bridesmaids and friend Anna Berglund as her maid of honor.

When Hefner proposed, he placed Harris's engagement ring in a music box that played the theme from her favorite movie, The Little Mermaid. She is carrying that sense of whimsy to her big day.

"Usually, weddings just have two main colors," Harris says. "We just want it to be colorful and pretty and the backyard is full of colors. We have the koi pond, and the fish and the birds are all different colors, so we just want to fit it all together and make it look nice and pretty."