This usually means that the character is depressed,  This has happened with my families on several occasions.  An example - in one of my families, the dad passed away.  I started the next generation by bringing home one of the sons.  His status code was "a bit blue".  I gave him fruit, vitamins, and candy.  His status immediately changed to "happy" after receiving a marriage proposal and accepting it 

     Sometimes a child is "a bit blue" when he or she is the only child and a brother or sister is born.  I give the child fruit or candy and send him (or her) outside to play.  This usually works for me!