I don't think they are truly white... Bulldogma has one. they are mottled splash, resulting from breeding 2 mostly blues (very little red/brown coloration) together. but (when they're clean) you can see white tips on the off-white or lightly grey feathers. a true dominant or recessive white is not a SFH but likely something from an outcross. if you breed one of these mottled splash birds to a black-based one, you SHOULD get all blue-based mottled birds. if you get anything else, then it's a mix.ki4got, I have seen people have white Swedish, is that not considered a standard color? I just noticed it wasn't included in your list.
this is a mottled splash cochin, for comparison. same breeding as the roo pictured just below her. she has darker hackles than many splash birds do, due to the melanizing gene she also carries...
currently she's bleached out to more of a dirty white color, but if you look closely on the pic you can see some white feathers and white tipped feathers mixed in with her light silvery ones. I had intended on breeding her to my black mottled cochin roo, but lost him a few weeks ago. so now we just have the mottled blue roo for all 5 girls (solid blue pullet & 2 black mottled pullets). LOL once the pens are done he'll be happy.