This question has probably been asked and answered before. However, there is another issue in setting up the data.
The OP is creating the data by
d <- data.frame(x = 1:10,
y = 1:10,
col = c(rep("red", n = 5), rep("green", n = 5)))
This results in an alternation of the two colours
d
# x y col
#1 1 1 red
#2 2 2 green
#3 3 3 red
#4 4 4 green
#5 5 5 red
#6 6 6 green
#7 7 7 red
#8 8 8 green
#9 9 9 red
#10 10 10 green
Reason is that n is not a defined parameter to the rep() function. According to ?rep, valid parameters are times, lenght.out, and each.
Probably, the OP has meant
d <- data.frame(x = 1:10,
y = 1:10,
col = c(rep("red", 5), rep("green", 5)))
which results in successive rows being coloured in the same colour:
d
# x y col
#1 1 1 red
#2 2 2 red
#3 3 3 red
#4 4 4 red
#5 5 5 red
#6 6 6 green
#7 7 7 green
#8 8 8 green
#9 9 9 green
#10 10 10 green
By the way,
col = c(rep("red", 5), rep("green", 5))
can be written more clearly as
col = rep(c("red", "green"), each = 5)
With this, the following plot statements
library(ggplot2)
# variant 1 (OP's own answer)
ggplot(data = d, aes(x = x, y = y)) + geom_point(colour = d$col)
# variant 2 (aosmith' comment, more "ggplot2-like")
ggplot(data = d, aes(x = x, y = y, colour = col)) + geom_point() +
scale_colour_identity()
produce the same chart:
