To produce two plots on the same image, all you have to do is change the plot function to a lines function when you draw the second distribution. Here is a rather long example.
leftxlim = 60
rightxlim = 130
mean = 95
SD = 2
#Two tailed test plotting
bt<-seq(leftxlim ,rightxlim,1)
plot(bt,dnorm(bt,mean,SD),type="l",main="Two tailed test", xlab = "", ylab = "")
left.tail.xval <- qnorm(0.025, mean, SD)
right.tail.xval <- qnorm(0.975, mean, SD)
abline(v=left.tail.xval)
abline(v=right.tail.xval)
cord.x<-c(leftxlim ,seq(leftxlim,left.tail.xval,1),left.tail.xval)
cord.y<-c(0,dnorm(seq(leftxlim ,left.tail.xval,1),mean,SD),0)
polygon(cord.x,cord.y,col="skyblue")
cord.x1<-c(right.tail.xval,seq(right.tail.xval,rightxlim,1),rightxlim)
cord.y1<-c(0,dnorm(seq(right.tail.xval,rightxlim,1),mean,SD),0)
polygon(cord.x1,cord.y1,col="skyblue")
cord.x2<-c(left.tail.xval,seq(left.tail.xval,right.tail.xval,1),right.tail.xval)
cord.y2<-c(0,dnorm(seq(left.tail.xval,right.tail.xval,1),mean,SD),0)
polygon(cord.x2,cord.y2,col="red")
leftxlim = 60
rightxlim = 130
mean = 85
SD = 2
#Two tailed test plotting
bt<-seq(leftxlim ,rightxlim,1)
lines(bt,dnorm(bt,mean,SD),type="l",main="Two tailed test", xlab = "", ylab = "")
left.tail.xval <- qnorm(0.025, mean, SD)
right.tail.xval <- qnorm(0.975, mean, SD)
abline(v=left.tail.xval)
abline(v=right.tail.xval)
cord.x<-c(leftxlim ,seq(leftxlim,left.tail.xval,1),left.tail.xval)
cord.y<-c(0,dnorm(seq(leftxlim ,left.tail.xval,1),mean,SD),0)
polygon(cord.x,cord.y,col="skyblue")
cord.x1<-c(right.tail.xval,seq(right.tail.xval,rightxlim,1),rightxlim)
cord.y1<-c(0,dnorm(seq(right.tail.xval,rightxlim,1),mean,SD),0)
polygon(cord.x1,cord.y1,col="skyblue")
cord.x2<-c(left.tail.xval,seq(left.tail.xval,right.tail.xval,1),right.tail.xval)
cord.y2<-c(0,dnorm(seq(left.tail.xval,right.tail.xval,1),mean,SD),0)
polygon(cord.x2,cord.y2,col="red")