Bash prompt in OS X terminal broken

PS1="${BLUE}u${CYAN}@${RED}h${BLUE}wn[${red}$${NC}]"

function _my_prompt ()
{
  # magic goes here
  my_prmpt=....
}
PROMPT_COMMAND='_my_prompt'
PS1="[$my_prmpt] $"

PS1="${BLUE}u${CYAN}@${RED}h${BLUE}wn${red}$${NC}"

PS1="${BLUE}u${CYAN}@${RED}h${BLUE}w${RED}rn$[${blue}]"