Not weird genetics--pretty straight forward, actually. You just don't know the genes your birds carry and how they mesh together.
White in silkies (and showgirls) is almost always recessive white, which hides all colours and patterns that are genetically present. It is essentially and OFF switch. Because white has been bred to white for generations, and all other colours and patterns are not visible, they have not been selected for or against. With the exception of having two copies of the recessive white gene, no two recessive white birds carry the same set of colour and pattern genes. Colouring of offspring therefore is completely unpredictable.
If you remove recessive white from the geneset (by breeding to a non-white bird) you will get all sorts of outcomes, and a 2nd generation will reveal even more. This information about recessive white is covered at least once a week in various posts.
Yellow or creamy down does not necessarily mean a white bird--if can, but it can also indicate other colours. Most simply, it indicates that the bird carries at least one copy of gold, possibly two. It can also indicate that the bird is wheaten based (but not always), and rarely in silkies. There is also a gene for snow white down that silkies sometimes carry. I don't believe it has any relationship to adult colouring, although I do not have a lot of information about this particular gene.
Splash silkies often have creamy down with some yellow. Lighter blues can come from creamy/yellow down.