you are right, you can't produce spector ivory cause they are on the same loci.

Just like you can't produce a Lesser Super Mojave. no ?
I know this is getting OT, but the reason there is still some doubt about the Yellowbelly and Spector being on the same loci is because, as AaronP said, Superstripe x Normal breedings produce normal offspring in addition to YBs and Spectors. You don't see this when breeding, say, a Blue Eyed Leucistic which was made from a Mojave and Lesser to a Normal- you only get Mojaves and Lessers in the resulting clutch. If Spector and Yellowbelly are on the same allele in the same way the Mojave and Lesser are, then when breeding a Superstripe to a normal you should produce ONLY YBs and Spectors. That's why I added the caveat to my answer. Crazy weird genes

ANYWAY Mystic x Pastel Mystic

Normals
Pastels
Pastel Mystics
Pastel Super Mystics
Super Mystics