Plot with two different coloured regression lines and legend

It is a trivial problem, but in the book I couln`t figure out how to put
different colours at different regression lines 

plot(bif,abund,type="n", xlab= "number_bifurcations", ylab="abundances")
sbif<-split(bif,stage)
sabund<-split(abund,stage)
points(sabund[[2]],sbif[[2]],pch=16, col="red")
for(i in 1:2) abline(lm(sabund[[i]]~sbif[[i]]))

Thanks in advance
Yvonne Fabian

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