Actually, with ANY polymer clay, you need to condition it BEFORE using it. The only exception is the translucent clay, which you don't want to work too much before using.
I have found that I take the color I want to use...and add a tiny amount of white (like a small pea size ball) and blend until there is no white left...then I KNOW it is conditioned.
Conditioning is needed whether you use Premo, Fimo (Soft or Professional), Kato, Cernit, or Pardo...
This link talks about conditioning... http://www.polymertutorials.com/catalog/polymer-clay-condition-tutorial.php
Jodie in AZ