I did it just to make you scratch your head Munky!
No, I'm joking… When you need to have white, but you are starting with loud colored plastic (red, silver, black for me). It is easier to transition using a grey in-between layer. The reason is that grey covers waaay better than white. If you spray white only, it'll take more layers to get to that even white color. So if you spray grey first, you get that easy coverage muting the loud colors, then you can get an easy spray coverage of white to finish off.
If the plastic had been a standard kit color (off-white etc), Then I would just use white since I didn't have to tackle masking/covering a loud color.
More ranting and babbling… blah… sorry...
lemme know if you have questions.
16. July at 23:00:33