What does it mean when a company trademarks a color?

While brushing my teeth and absentmindedly reading the back of my bottle of Listerine, I noticed this: “The bottle design and purple color of this product are trademarks of Johnson & Johnson”.

A trademarked color? Wtf? Does this mean that the company is claiming ownership of a very specific shade of purple, or does it only apply to colors of mouthwash so that others can’t mimic the product?

I’ve heard of Cadbury claiming deep purple, Tiffany blue, etc…