People come to know that blue is a color. A color of sadness, calmness, sea and many other meanings that could be associated with blue.
Reaching blue means reaching calmness in your heart.
When can one reach this?
Well, it will always depend on the individual but one thing is for sure. You'll reach blue when you get contented of what you have.
Contentment in one's individuality is the key to reaching blue.