None Material... is actually a material?

Story time. I was creating a simple FPS counter UI to display Current, Min, Max and Average FPSes, and I wanted the colour of the text to change dependent on the FPS value.

I know where I went wrong (and have since altered the code), but the script originally assigned the material's colour to be the colour I wanted. So it would say something like text.material.color = Color.Green;

I was confused for a while why all my text, and some other images, were changing to the colour that was being set.

Today the answer may have hit me: the material of everything that was changing colour was set to 'None'. Before I had assumed that any object that had the 'None' material just had it's material property set to null, but I guess it's more of an 'empty' material instead?

So I guess my question is: Is this a bug or a design decision by the Devs? If it's the former, then I'd be curious if anyone else has had the same happen to them, and if it's the latter, I'd be interested to know why it was made not read-only.

I've had a quick google but couldn't find much relating to the 'None' material.

Cheers,