Pastel Motley?

What exactly is a pastel motley? Is it the same as a ghost motley (or something else?), or is it a morph of its own?

It is a ghost motley. It is referred to as a pastel as the motley trait tends to bring out a more pastel colour in them than would be normally found.

I've also seen some anery motleys referred to as pastel for their bright corals/pinks that come in as they age. Anery mots can very much resemble ghosts in lightness and may be impossible to tell from ghost motleys without known parental genotypes or test crossing.

In my opinion, it's a description of a coloration moreso than a specific genotype. Not everyone's definition is the same, so if you're buying one be sure to ask the seller/breeder in advance before purchase if genotype is important to you.