Invisible earnings

Q1. What is "*invisible earnings*"? I can't find out the meaning or example sentence in my dictionary. Is it some 'profits related to mind or spirit'?

Q2. My dictionary says "*invisible green*" is "very dark green". How can it be so? Doesn't 'invisible' mean 'transparent'? So 'Transparent green' is 'light green, isn't it? Would you explain why not?