Why make randomColor() an instance method instead of a static method?

That makes perfect sense. The "start from zero" approach has been very helpful even with my programming background, since it's been a few years since I fully flexed those muscles.

Often in programming there are things that seem more convenient at first, but that convenience comes with a hidden cost that you don't discover until later. Global variables come to mind. I wasn't sure if this was that sort of thing - to me a static method was the obvious solution, but I don't know enough about iOS development to know if there's a good reason not to do it that way, or if this approach would be more beneficial in future examples that are much more complex.

Actually, as I am responding I thought of maybe an example of that - say you're fetching your array of random colors from a server, rather than hard-coding it in the class. In that case, I assume you would fetch the data from the server in the init() method, which wouldn't be run unless you create an instance of the model first. Is that correct?

In that scenario, you could pass in the data from the server to a custom initializer, init(colorData: [Colors]), for example. In Swift, initialization is a tricky topic and there are some very strict rules (as compared to ObjC). An instance cannot be created without all stored properties being assigned initial values in the init method. The only exception to this is unless the properties are marked as optionals, making them default to nil.