The chosen ace is shown to be "odd" because it’s the only RED backed card in the BLUE backed packet!
A different ace is chosen and this second selection now becomes the new "odd" card because it’s the only BLUE backed card backed card in the RED backed packet!
The first "odd" card has a red back and the second "odd" card has a blue back.
The two remaining cards also prove to be "odd" because their backs are YELLOW and GREEN!
All four Aces have different colored backs!
Everything can be examined and you are instantly reset.