JSON Files & Thunkable Variables

Hi!

I don’t understand at all why when reading a JSON File, if I assign the result of the reading to a “orange” variable, I get an error! See picture below.

On the contrary, if I’m assigning the result of the reading to a “green” variable, then everything works fine ! See picture below.

I guess I’m not understanding the difference between these two kinds of variables ?

Could someone explain me this feature? Thks in advance!