I don't think the crystal blue should be illegal, given that most new prestige cars have zenon/blue headlights which look a blueish colour. As long as the lights put out a colour temperature within given values (say 2000k to 7000k) I don't think there should be a problem. Perhaps the legislation is not tightly focused enough to specify values, and the Police think that any colour other than translucent is illegal.
I guess my point is that I don't really know why the authorities don't allow it, but I just don't really see any point to having red,green,purple coloured lenses, other than someone, somewhere must think they look cool??? The coloured lense covers I've seen have mostly been on the typical "BnS" utes with no fat chicks stickers & kenworth mud flaps, so you can see where I'm coming from....