when is CD1?

Charlotte • 26, married for 2 years. Mummy to Felicity who we lost at 22weeks 6/3/16. Rainbow due 3rd Sept 17
So I had light pink/brown spotting yesterday. It was very very light though. Today I have started AF properly.
I was just wondering, what would you call CD1? The day you start spotting or when you start bleeding "properly" i.e. red blood?
I know it probably doesn't matter really I was just wondering what others do.