Can anyone tell me if this is painted on and if it's pearl dust on deep blue luster dust?

I appears to be painted on because very slight streaking can be seen on the second tier.  It could certainly be done with a dark blue luster dust or a dark blue petal dust with pearl dust applied over it with a dry brush.

I am going to use blue fondant.  I would just just the pearl dust, correct?

That sounds like it would work.  Perhaps try it on a small piece of fondant first to be sure it gives you the look you want.