There are miltiple allelic mutations found on the recessive white c allele and at least one sequenced non-c recessive white based on the mottling allele.
I have figured a better explanation. I've been doing a lot of research on shank colors and white plumages. The hen is blue shanked but totally white. According to my research if she were c/c recessive white, it would give her lighter shanks. This makes sense since I believe that she comes from hatchery stock cross parentage, white d'uccle, crossed into a white booted bantam line. There is also a possibility that she has dominant white, from the hatchery stock or from a golden neck (buff mottled) cross into the line. I believe the male; also pure white is recessive white with white legs. He is probably homozygous for Id gene for inhibition of dermal melanin, although he could be heterozygous. I don't have enough experience with that gene to tell just by looking at him, or from the F2. If he is, the recessive white would dilute the melanin to where it would be hard to tell. SO, long story shortish, I think that I'm looking at one (or possibly both) birds which are carrying recessive white (1 homozygous and 1 hetero, possibly). I believe that I have one bird homozygous for recessive white and one bird heterozygous for it. This is a guess. I also believe that one of the birds is heterozygous for dominant white, (or both could be). After hatching as many chicks from the pair as possible, the outcomes mirror the statistical probabilities of several different variations, but in general it is 50/50 with red leakage, possibly mostly in males but many are too young still to sex. I believe that these birds either are C or c for recessive white and are on an e^b/e^b, e^b/E or E/E background and without other melanizers are showing the gold leakage in the same way as a black bird does without those melanizers, especially in males. The dominant white is covering the E (black) allele phenotype with white but is unable to cover the gold leakage. Also the gold is diluted, which dominant white does.
The harder issue is come up with a breeding plan to try to get the recessive white homozygous and maybe even to eliminate the dominant white? I'm not sure it's doable, or even necessary. I may be forced to do genetic testing, or even doing outcrosses with other colors to attempt to get back to the usual genetics. Usually, white booted bantams have been mille fleur under the recessive white, or at least that is the original recipe based on their long ago history of having those two colors in the breed (at least in the US). There is an outfit in Miami which does testing by blood, eggshell or feather. I haven't heard of anyone using them and a little reticent to trust it. I don't know if the eggshell testing tests the hen or the chick it hatched from. I would guess it is the hen that laid the egg.
The bottom line is that mixing recessive genes for white with dominant white is a risky proposition, especially in rare breeds which are difficult to find (without unknown parentage). It might seem like an easy fix, but it isn't. Without knowledge of the parentage it's a crap shoot, especially with a recessive gene that hides cryptomeres and a dominant one which covers many phenotypical characteristics. DON'T DO IT, unless there is a good reason and unless you know exactly what you're working with.