[R] axis colors in pairs plot

[Anne York]

The following command produces red axis line in a pairs 
plot:

pairs(iris[1:4], main = "Anderson's Iris Data -- 3 species",
pch = "+", col = c("red", "green3",  "blue")[unclass(iris$Species)])


Trying to fool pairs in the following  way  produces the 
same plot as above:

pairs(iris[1:4], main = "Anderson's Iris Data -- 3 species",pch = "+",
col = c("black", "red", "green3", "blue")[ 1+ unclass(iris$Species)])

One very kludgy work-around is to define a new level 1, say 
"foo" in the first row of iris:

iris2=iris
iris2$Species = as.character(iris2$Species)
iris2$Species[1]="foo"
iris2$Species = factor(iris2$Species)

pairs(iris2[1:4], main = "Anderson's Iris Data -- 3 
species", pch = "+",
col = c( "black","red", "green3","blue")[ unclass(iris2$Species)])

However, if any other row is redefined, the red-axis 
persists. For example:

iris2=iris
iris2$Species = as.character(iris2$Species)
iris2$Species[3]="foo"
iris2$Species = factor(iris2$Species)


pairs(iris2[1:4], main = "Anderson's Iris Data -- 3
species", pch = "+",
col = c( "black","red", "green3","blue")[ unclass(iris2$Species)])

I'd appreciate suggestions for a simpler work-around.

Thanks,
Anne