

Its Trademark Law in Australia.
For example Cadbury has a trademark protecting its purple (defined as pantone 2685C) from competitors in the chocolate industry. On the other hand Whiskas has one protecting its purple (defined as CMYK {40% C, 100% M) from competitors in the cat food industry.
Because its trademark law both only cover their specific industries (so purple would be fair game for a business in another field), but despite the precise definitions used for the colours they would be able to argue that a competitor using a similar purple could cause confusion in consumers, (so they effectively block out an area of the color spectrum).
I believe in must jurisdictions its the distribution that makes it an issue not the selling. If you started handing out your “Burger King” burgers in a public place I would expect to be shut down.