The background changes when Candace dives under a table to phone Phineas. Before the call, the room is kind of avocado in color but afterward it's tannish, the column shapes become different, the black vase disappears, and the archway on the right leading off to another room or foyer becomes a stage with a curtain. (Meanwhile, the white tablecloths, yellow chairs and people seated remain the same, although one man seems to have left during the phone call.)
The stage curtain changes color from a powdery sort of blue to deep blue.