everything is in the genetics
color of leaf and or buds
color of pistils as you said
how the pistil swells
plant structure, height,
weight of buds
ect ect ect

its up to the breeder in what traits they want to breed for, their might be a special odd looking trait you are looking for

if you really want to learn more about the genetics and other things check out the breeders bible by greg green, hands down the best cannabis book ive seen