I know this is an old thread, but I have been researching paint for a Beetle build for a few weeks now, which looks to be the same shade as the Scorpion for the most part. So I will share what I found here in case anyone else finds this thread.
Now, the lower tub on the Scorpion is yellow plastic on the newer models. I believe the older ones were black. The polycarbonate body on the original I remember had a metallic look to it. So if you are wanting the metallic look, you can spray a light coat of pearl white before applying the Tamiya colors listed below. Just keep it light, and allow it to dry very thoroughly before applying Tamiya paint if using an acrylic pearl under it. Tamiya paint is known to not play well with some acrylics.
Tags: Kyosho Scorpion Beetle Yellow Paint
Anyway...
I am trying to match the Beetle's yellow wheels, and the closest thing I have found for the polycarbonate body is two coats of 'Tamiya PS-6 Yellow' followed by a backer of 'Tamiya PS-56 Mustard Yellow', then backed with 'Tamiya PS-5 Black'.
Using either of these yellows by themselves is close, but PS-6 is too bright, and PS-56 is too dark. Using both looks perfect.
I will share pics and info in an upcoming build thread.