Pastels have a reduced pattern and a more or less clear yellow colour on their sides.

Some definitions of genetics...

Allele : alleles are the different versions of the same gene
Dominant allele : an allele is said to be dominant if he is able to pass alone a characteristic trait of the parents to the descendants.
Recessive allele : an allele is said to be recessive if he is not able to pass alone a characteristic trait of the parents to the descendants.
Co-dominant allele : alleles are said to be co-dominant when together they are able to pass a characteristic trait to the descendants.
Homozygous : An individual is said to be homozygous for a given gene if he possesses two identical alleles of this gene.
Heterozygous : An individual is said to be heterozygous for a given gene if he carries two different alleles.

Pastel gene is co-dominant.

male	female	descendants
Pastel	Pastel	50% of the descendants are Pastel 25% of the descendants are normal 25% of the descendants are Super Pastel
Pastel	normal	50% of the descendants are Pastel 50% of the descendants are normal
Super Pastel	normal	100% of the descendants are Pastel
Super Pastel	Pastel	50% of the descendants are Super Pastel 50% of the descendants are Pastel
Super Pastel	Super Pastel	100% of the descendants are Super Pastel

Few possible combinations :
Pastel x Mojave
Pastel x Spider (Bumblebee)
Pastel x Pewter
Pastel x Ghost