I believe I have tried real olive oil, straight from a farm in Greece and it is very dark green, great tasting and and no real burn at all, just a light tickling in the throat. Burning means that it is probably going rancid. Oils with a higher acid level are lower quality and burn more.
Green olives will have a fruitier taste and make a greener oil. Black olives are ripe and will make lighter oils, many times these are olives picked after fallen to the ground, already starting to go bad. Green olives are healthier.