Knowledge: The color of Starbucks is often used only green even though it is white and green. On the other hand, iron oxide is red because of the reaction to air exposure.

Conversation:
I love the color red. It is so vibrant!
Alright! Did you know Mars is red because of iron oxide?
No, I didn't! How is that colour though?

Response: Ah, that is because of the reaction to air exposure on iron oxide.