Silkies are one of the most difficult breeds to sex before 4-5 mos. of age and sometimes not till they crow or lay eggs. Are these hatchery stock or from a silkie breeder? I ask because the middle one has a very odd comb - looks like it wanted to be a walnut(proper) comb and then grew a tail on the end. The third bird has a big walnut comb for such a young age.
The black chick may possibly be a pullet - but, at this age it is a wild guess. The coloring is confusing as well. The black chick looks to be changing to possibly blue but, I've never seen it start on the head.. Head is usually the last place it changes - with blue coming in on lower body first.
If you could repost new photos when they are 4 mos. of age - you will likely get much more accurate assessments. They are cute as the dickens.