That's right. Axel dyes his hair with Ketchup. The secret is out. That's not his natural hair color. He didn't get it done at a salon. He didn't do it with hair dye from a beauty supply store. He did it with Ketchup from his pantry. Really really cheap ketchup. It started as an accident. He used to be blond. He and another member of Organization XIII got into a food fight and the next thing anyone knew, Axel was a red-head.
He doesn't smell like Ketchup. The smell washes away but the color doesn't. Sure, it fades over time but that's why Axel's pantry is stocked with cheap Ketchup. He buys it in bulk to keep fooling the masses. Saix dyes his hair with Kool-aid but that is another story.