No, the clouds and sun just help as part of communication.
B=yesterday was terrific, so I'm in a fine mood
A=good things ahead today, so I'm in a good mood
C=yesterday was hell, so I'm slowing down
D= bad things today, I don't feel like it!

It was a didactic illustration for a non-fiction book on psychology

I guess the meaning is the mood depends on the weather right ^^