When two sex linked colors are bred together, the male offspring will be blue split the colors of the parents and the females will be the color of the father. Let's use Peach and Purple as our two sex-linked colors.
Peach male x Purple female = Blue split Peach/Purple males and Peach females
If you were to go insane and decide to breed the children of the pairing above together, it would be awesome and look something like this:
Blue split Peach/Purple male x Peach female = Peach males, Blue split Purple/Peach males, peach females, purple females
A note on Peach color: The current theory is that Peach is an interaction of the Purple and Cameo colors. If that is true, a Peach bird will necessarily be "split" Purple and Cameo, and could produce either when bred.
Peach Male X Purple Female = Purple Males split to Peach, and Peach Females. This is because "Peach" results from a Z chromosome containing both the Purple and Cameo mutations due to
crossover. As such, Peach is genetically Purple-Cameo. If a male homozygous for Peach (and is thus genetically homozygous for Purple-Cameo) is crossed with a Purple female, then the sons will have one Z chromosome from Dad with Purple-Cameo, and one Z chromosome from Mom with just Purple. Since there are two copies of Purple, that color will show. But because there is only one copy of Cameo, that color will not show. The result is that visually the sons will be Purple, but genetically be Purple split to Peach.
This is different from a Blue split to Peach male, which will have one Z that lacks either the Purple or Cameo mutation (thus a "normal" Z), and another Z which has both Purple and Cameo (they are not alleles). Blue males split to Peach which are bred to Peach females can have Blue, Peach, Purple or Cameo daughters. The Blue daughters inherited their Dad's original Z with neither mutation. The Peach daughters inherited their Dad's original Z with both mutations. The Purple and Cameo daughters result from inheriting Z chromosomes which underwent crossover during spermatogenesis (a normal occurrence) that occurred at a point between the loci of the Purple and Cameo mutations. This causes a swapping of chromosome material between Dad's two Zs, allowing the two mutations forming the Peach phenotype to separate. If crossover occurs at any point between the Purple and Cameo loci, the newly-formed Zs will have EITHER Purple OR Cameo, rather than EITHER both together OR none.
Look up the "
History of Peach" via Leggs Peafowl. Clifton Nicholson bred a Cameo male to a Purple female. Sons from this mating were IB split to Purple and Cameo. They appeared IB because they had only one copy of each mutation, but neither of them had a "normal" Z chromosome -- one Z had Cameo, the other had Purple. These sons were then mated back to their mother.
"This mating produced eleven peachicks which included three India Blue (2 males and 1 female), three Cameos (females), four Purples (2 males and 2 females) and one Peach (female). This was the first Peach produced."
Note the resulting offspring. The IB males did not inherit their father's copy of Purple, and so did not show the color. Some daughters were Cameo (inheriting their Dad's one Z with that mutation), and some were Purple (inheriting their Dad's other Z with the other mutation). But what did the IB and Peach daughters inherit?
The IB daughter somehow got a Z from Dad with neither Cameo nor Purple. The only way that could have happened is if crossover occurred between Dad's two Zs at a point between the Cameo and Purple loci. The result was two recombined Zs -- instead of one with Cameo and one with Purple, we had one with neither and one with both. That's how the IB daughter got a Z with neither mutation. There is no other way that an IB daughter could result from this mating. And that's how the Peach daughter got a Z with both the Purple and Cameo mutations.
Just as Purple and Cameo can combine onto one chromosome during crossover in a male split to both, they can also separate again in a male split to Peach -- but ONLY in IB (or any other Non-Purple, Non-Cameo color) split to Peach males. This is because in order for the mutations to separate, another Z must be available with NEITHER mutation. If crossover occurs in a male with either mutation on both Zs, you'd never know it because the result would be the same. For example, a Purple male split to Peach has two Zs with Purple, and one of those Zs also has Cameo. If crossover occurred and the Cameo gene switched over to the other Z, it will still be on a Z which also contains Purple. Males which show neither Purple, Cameo nor Peach but are split to Peach will thus have one Z with neither mutation. These males, when bred to any other females, will have daughters that are IB, Peach, Purple and Cameo (the frequency of the latter two will be dependent upon the frequency of crossover at points between the Purple and Cameo loci). Breeders have posted here that they have experienced this, and this would not be possible if Peach was a separate mutation rather than being genetically Purple-Cameo.
In terms of "what can you get?", an IB split to Peach male (one "normal" Z, one Purple-Cameo Z) bred to an IB female will result in the same diversity of daughters (IB, Peach, Purple and Cameo) as an IB split to Purple and Cameo (one Purple Z, one Cameo Z). The difference is in the ratios. An IB split to Peach male will be more likely to have Peach daughters than Purple or Cameo daughters. An IB split to Purple and Cameo male will be more likely to have Purple and Cameo daughters than Peach daughters. This is because the "less likely" daughters require inheriting recombined Zs with a crossover point between the two loci, while the others inherit their Dad's Z as-is.
There is extensive information out there on crossover inheritance with respect to sex-linked mutations in other bird species. This is how we have Cinnamon-Pearl and Lutino-Pearl cockatiels (Cinnamon, Pearl and Lutino are all sex-linked mutations, the genes lying on the Z chromosome). The process is the same. The frequency will vary with respect to the distance between the two loci -- the further apart on the chromosome the mutations are, the more likely the crossover point will occur between them.
A male cannot be "Blue split Peach/Purple." A male CAN be split to Purple. A male CAN be split to Peach. But remember that if he is split to Peach, genetically he has one copy of Purple and one copy of Cameo together on the same Z chromosome. If he had Purple on one Z, and Peach (i.e. Purple AND Cameo) on the other Z, he would LOOK Purple. He wouldn't LOOK Blue.
A Peach male is NOT split Purple/Cameo. "Split" means a bird is heterozygous for a mutation -- i.e. it has only one copy of the mutation, and one copy of the "normal" version of the gene. Peach males are homozygous Purple-Cameo. They have two copies of each. They are not split for either. Peach males can produce Purple or Cameo offspring ONLY when bred to females who show either of those mutations. A Peach male bred to a female that is neither Purple nor Cameo will NOT produce Purple or Cameo offspring. However, a Non-Purple, Non-Cameo male split to Peach can.
