So much for a white wedding.

Ashlee Simpson and Pete Wentz have told their guests "to dress in dark colors" to their nuptials on Saturday, a pal of the couple revealed to Usmagazine.com.

"[Guests] have been asked to wear cocktail attire, but to not be overdressed," added the pal.

On Thursday, crews erected a massive white tent with bright red curtains in the backyard of Simpson's parents' Encino, California home.

Also set up: a seating area around a fireplace adorned with a cross. (Similar to the altar Jenna Bush married in front of last Saturday)

Two oversized delivery trucks were also spotted at the property and the pool was covered to be converted into a seating area.

Simpson, who is about four months pregnant, will walk down the aisle in front of "around 250 guests" the pal told Us.

Guests are still being kept in the dark about details.

"Proper invites have not been sent out but instead guests have been given a save the date notice," a source told Us Weekly.

The rehearsal dinner – described by the source as "an intimate affair" for "family and close friends only" – will take place on Friday.