from what I understand, this is how it's done in a professional paintshop:
First, after priming, a coat of gloss black is added, and left to dry. 
Then to create the pearl effect, they generally mix 2 metallic colors, say, blue and red, and dilute this mixture extremely. ( 90 % thinner to paint ratio is not uncommon )
they will spray this in several thin layers, and top it with a gloss cote. 
I am yet to experiment with this though, and I wouldn't do it on a tamiya kit yet lol.. I'd probably buy a heller or airfix kit to practice on. 
hth, 
Richard Renes