I can’t tell the difference. Can you tell the difference?

Last night before turkey dinner, I was making some drinks. Rum and (sugar-free, calorie-free) cola. I started making mine with Diet Coke, but my brother insisted he wanted his with Coca-Cola Zero. So I looked at the labels, and I blinked. Then I read the ingredient lists of both, and I blinked again. Then I scratched my head, and blinked once more. Huh? I can’t tell the difference. Can you tell the difference?

Diet Coke
Ingredients:
carbonated water, caramel colour, phosphoric and citric acid, aspartame (contains phenylalanine), flavours, sodium benzoate, caffeine, acesulfame-potassium.
Nutrition Facts, per 250ml: sodium 35mg, protein 0.1g

Coca-Cola Zero
Ingredients:
carbonated water, caramel colour, phosphoric acid, aspartame (contains phenylalanine), potassium benzoate, natural flavour, potassium citrate, acesulfame-potassium, caffeine.
Nutrition Facts, per 250ml: sodium 30mg, protein 0.1g