Yes. Any other questions? Lol. Your correct, all of those have an effect on the darker syrup. The warmer the tree, sap and air temperature, bacteria goes up and sugar decreases, which basically adds to boiling time which also increases the dark coloring. However, instead of grossing out the customer with the bacteria explanation (unless you can determine that it won't), just say the warmer it gets in the spring, the more the sap composition changes, which makes the darker syrup. And the dark does have a stronger flavor.

Steve