When Derek asks Meredith to kiss him before his surgery, he is pale with dark circles under his eyes and almost white lips. Later, during surgery, his complexion seems far healthier.
When Meredith holds up the pregnancy test near the end, it is clearly a sticker.
When Christine and April are looking for a surgeon for Derek, Jackson comes out of the OR and startles them and they duck down. When they realized he wasn't the shooter and stand up, Christine plainly calls Jackson "Jesse".