If you breed a Desert X Bumble bee it should be:

1/4 bumble bee het. desert
1/4 spider het. desert
1/4 pastel het. desert
1/4 normal het. desert

Basically all offspring will either appear bumble bee, spider, pastel or normal and just carry the desert gene because desert is recessive. You'd have to breed one of the offspring back up to the dad to make visual deserts/combos.

(I'm pretty sure thats how it works, someone correct me in I'm wrong)

I'm tired so I won't even go into bringing pied in the mix...