Nothing is a no-brainer for me. Sometimes I need it spelled out. After a few trips up and down an elevator I did start to figure out one thing. Green means open and black means close. The characters look very similar, so this was an easy way for me to remember.
Of course Dek figured it out right away. He is not even two.
So one day when you are confused, you can look back on this and have your ah-ha moment too.