Smooth Mule, your chick phenotype could have easily hatched out of my sex-linked spotty pens (particularly the white patch on the back, also sometimes white patch on head).

* Left e+/e+ spotty & Right ER/e+ spotty

See this thread on Barring locus "New 2017 B locus paper - 3 mutation alleles"
* This discusses B^Sd sex-linked dilution and the newly discovered B locus allele Sex-linked Extreme Dilution. The latter day-old chicks when heterozygous on E have the white patch on the back, plus back of head too.

Also, Lanae was segregating similar spotty phenotype in Arauacanas to my Australian pitgames:
But these were crossed back to wheatens, so on a different E locus allele, chicks were white.