Everytime Luke or Leia get angry or do something questionable like choke someone, their eyes light up red.
For example when Luke is moaning about wanting to go to Toshi station or the Academy his eyes light up.
When Tarkin announces that he is going to blow up Alderaan anyway Leia’s eyes light up red.
This happens even if they are in disguise like Luke when he is wearing the Stormtrooper helmet or Leia when she is dressed as a Bounty Hunter in ROTJ.