Cody and his model wife, Danny Pimsanguan, were pretty confused at their gender reveal party ... when they cut open a cake expecting to see blue or pink.

But they didn't. It was plain white.

"We’re having a white kid! It’s WHITE!!" Danny joked.

Garbrandt literally dug through the cake with his bare hands ... but still nothing.

Their friends eventually let 'em in on the prank ... and hooked Mr. and Mrs. Garbrandt up with a confetti-filled balloon instead.

Hilarious. Congrats!