Not like this lemon cuckoo Pekin?
http://www.freewebs.com/wellcottagepoultry/pekins.htm
Do you mean more like this colour? (sorry it's a bit blurred. )
I think 'lemon' cuckoo is a desceptive term. Citron/Zitron does translate to lemon in some European languages. And very often when the name lemon or citron is used it is referring to the cream gene, ig. As you mention, in the cream light brown dutch bantams or the lemon mille fleur the gene is...
I think it a case of hobby names again. In this case I don't think the 'lemon' refers to the cream gene. Their colour is too dark for cream unless with mahogany or something. From what I've seen they are just buff birds with barring. I made buff cuckoo Orpingtons which appear to be the same...