Identifying an iPad/iPhone by Model Number The model number of an iPad/iPhone can be determined by going to:    

Settings app → General → About → Model Number

How to use this value (the one in ML2I2KN/A format) to determine the device type? It is an official model identifier from Apple, but how can one use it to identify their device? I didn't find any service of the kind at Apple's website.

If you tap on Model Number it will show another value - in format like A1652, and this value can help to find a general model at Identify your iPad model page (or similar for iPhone), but unlike ML2I2KN/A it cannot be used to determine color and storage capacity of the device.

There is 3-rd party service Everyi, but quite often it doesn't find anything. For example, searching for ML2I2KN/A gives nothing (I know it's iPad Pro 12.9 from 2015, but that's not the point).

Simply googling this value will highly likely result in some store's website with the correct item specification, and there is also this wiki page with quite an impressive table of models.

But is there any  Apple official resource for this purpose?
You can check this site, some products can be found here. Hover mouse over the model, capacity and color will be displayed like this. It seems that Apple only wants to distribute this information within the company, there is no more public information.
 http://salesdownload.apple.com/public/sites/asw/common/compliance/Other_iPad.htm