You need to use a gloss black base only on the four High-Shine Alclad 2 paints:
Stainless Steel
Chrome
Polished Aluminum
Aircraft Aluminum
All the other colors are not as shiny, ranging all the way to Dull Aluminum, and will work fine with any good filler/primer, such as Alclad Gray Primer and Microfiller or Mr Surfacer 1200. As mentioned before, a perfectly smooth surface prep with no dust, scratches or any other imperfections is the key.
"You can't have everything--where would you put it?"