
In dals lemon and orange spotting is due to a variant of the regular black or liver genes which affects hair colour and not skin pigmentation - in lemons the nose pigment is black, and in oranges the nose pigment is liver. (Confusingly they're the other way around in the US!) I would imagine that blue is a dilute black.
It's interesting that English setters have similar colour patterns and variations (and are also born white, apart from the patches, which are acceptable in their standard), as well as pointers still allowing blacks, livers, oranges and lemons. There must surely have been some crossbreeding back in the depths of history.
As you say, genetics is a fascinating subject.