as is my understanding of sex links -
black sex links use a 'red'roo , normally RIR or new hampshire ...the mother needs to be a barred rock. chicks will hatch out all black but the roos will have a white dot on their head and feather out with barred feathers with red flecks...pullets feather out black with red flecks round the neck
red sex links use again a RIR or new hamp roo..but you can use different mothers for different 'colours/crosses'
crossing a rir/new hamp roo with a white rock hen will give you gold comets
RIR/new hamp roo x SLW hen = cinnamon queens
RIR/NH roo x RIR hen - red sex links (pullets will be red/buff, roos white)
RIR/NH x delaware or production red = red sex links (pullets red/buff/roos white)
it goes a lot deeper than this but these are just a few examples i found on the web,there are many more possible crosses!