The grey is there because it is cheap. It is clear that this is the case.
Hasbro has been using this for years and since Matty decided to cheapen out in their 'Collector grade' lines for the last year, they have been substituting whites and silvers for it just like Hasbro. Recently they decided that 'Snow' should be an ugly grey instead of white and that Uncle Sam is not longer Red, White and Blue but Red, Grey and BlueThe red and Blue are also that dull shade that Hasbro likes to use.
Clearly some paint colors are 'cheaper' than others in manufacturing.