I suspect they wrote a new init function specifically for Swift (as an extension), but I could be wrong.

They have a concept of implicit/explicit "external parameter names".

The docs definitely indicate that some magic is occurring but they don't say exactly how. Perhaps If the first parameter contains the word "With"?

They do explicitly state that initializers will get "init" and "initWith" stripped off and whatever follows becomes the first parameter. The fact that "colorWithRed" is translated to "red" might indicate that it is looking for the keyword "With"