R par set cannot be changed

Question

I wonder how I can use the par set of no.readonly normally.For the following code,

par1 <- par(no.readonly=TRUE)
set.seed(2015)
xx<-rnorm(100)
par(pch=17,col="red")
plot(xx)

par2 <- par(no.readonly=TRUE) # par2 pch=17,col='red'
par(pch=17,col="blue")
plot(xx)

par(par2)
plot(xx,main="why the color is black not red?") 
# why this time the col is default 'black'?

Could someone help me use par to set the color red as before? Why this time par is invalid for col but useful for pch?

Answer 1

Your color is being overwritten by elements further in the list. For proof:

par(col = "blue")
par("col")
# [1] "blue"
par(fg = "red")
par("col")
# [1] "red"

(I'm not certain how many other oevr-riding elements there will be, but this is one that is likely impacting you.)

If you want to save/reuse "col" and "pch", perhaps you should save them (and not the rest of the list).