How do you sing?

Are you able to hear notes correctly in your head? From what I can tell the only difference between a good singer and a bad one is how accurately they hit the pitches. If all your intonations are perfect it really doesn't matter how your voice is colored because you sound like a musical instrument.

So with that in mind the key to good singing is that the voice you hear in your head is correctly pitched. Do the interior mechanics of your head prevent you from accurately interpreting pitches? In my experience it doesn't, but I might be "wrong."

Let me know your thoughts.