Continuity mistake: During the scene where Rachel puts Aidan into the bathtub at Max's house, he is wearing very light white boxer underwear as he is being put into the water. A little while later when Rachel pulls Aidan out of the bathwater, he is suddenly wearing very dark blue/navy colored boxers. Although water would darken the color somewhat, this is far too dramatic a change to be natural. The lighter color couldn't have possibly darkened to that extent. They are two different pairs of boxers.
Picture added & edited by Hamster