Blue color nice?

BLUE is a nice color isn't it?but why when ppl sad they use the phrase 'feeling blue', 'once in a blue moon'.seems like phrase with the word blue represent smtg not so good.feeling blue is how I feel now.Recently seldom get mad, get frustrated, less arguement and of course less moody.I duno wat make me so but it's a good thing,rite?Today smtg get up.I've get to know smtg tat I dun need or cannot know and this breaks my heart.Suddenly feel so bad that I dun hv entrusted image in ur heart, I din expect to know all secrets but at least smtg related to u.For me, it's kind of 'sharing is caring'. or maybe without knowing tis less worry and tat's wat u wan.Did I expect too much that I wish to share happiness and sadness.I understand that even if I know bout it I can't reli help but at least I can be and I am a good listener.Y din tell me?is it coz of u dun trust me?is it coz of I'm in the sensitive position?or is it coz u think that I cant keep tis secret?I'm reli very confused.If I cant even share problems and only can share happiness, then what am I really need for?What role am I playing in ur heart?What?Why?The onli answer I know is No idea.really don't know.