Bumble bee Ball Pythons are the result of the combination of 2 genes : Spider and Pastel.
So Bumble Bees have the pattern of the Spider associated with the yellow color of the Pastel.
According to specimens, the white from the belly recovers a more or less big part of 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.

male	female	descendants
Bumble Bee	Bumble Bee	37,5% of the descendants are Bumble Bee 18,75% of the descendants are Killer Bee 18,75% of the descendants are Spider 12,5% of the descendants are Pastel 6,25% of the descendants are Super Pastel 6,25% of the descendants are normal
Bumble Bee	Super Pastel	25% of the descendants are Bumble Bee 25% of the descendants are Spider 25% of the descendants are Super Pastel 25% of the descendants are Pastel
Bumble Bee	Spider	37,5% of the descendants are Bumble Bee 37,5% of the descendants are Spider 12,5% of the descendants are Pastel 12,5% of the descendants are normal
Bumble Bee	Pastel	25% of the descendants are Bumble Bee 25% of the descendants are Pastel 12,5% of the descendants are Killer Bee 12,5% of the descendants are Spider 12,5% of the descendants are Super Pastel 12,5% of the descendants are normal
Bumble Bee	Normal	25% of the descendants are Bumble Bee 25% of the descendants are Spider 25% of the descendants are Pastel 25% of the descendants are normal