Why does ColorZilla need permission to "access data on all websites"?

When installing ColorZilla for Chrome, you might see the following prompt:

ColorZilla needs to be able to pick colours from any page in your browser. Because of the way Chrome permission system works, this means that ColorZilla needs permission to "access your tabs and your data on all websites" just to perform its basic functionality.

ColorZilla DOES NOT collect any of your data or your browsing activity on any websites. Your privacy is extremely important to us. You can read our Privacy Policy for more info.