The default colors in R (e.g., ggplot2) are not great, and indeed there are much better coloring schemes. This is one that is intended to be more visually distinguishable for people affected by color blindness:
colors <- c("#E69F00","#56B4E9","#009E73","#F0E442",
"#0072B2","#D55E00","#CC79A7")
These colors are based on this paper. See also here.
Here is a short R script demonstrating how to use it in ggplot2:
library(ggplot2)
colors <- c("#E69F00","#56B4E9","#009E73","#F0E442",
"#0072B2","#D55E00","#CC79A7")
data(iris)
iris <- transform(iris,Petal.Length = cut(Petal.Length,breaks = 0:7))
print(ggplot(iris,aes(x = Sepal.Length,y = Sepal.Width,col = Petal.Length)) +
geom_point(size = 2) +
scale_color_manual(values = colors) +
theme_minimal())