In the last few years, I’ve been using ggplot2 quite a lot. While the
ggplot2 default theme is quite slick, I started tweaking the theme to
fit my own taste and/or that of the target audience.

artyfarty is a collection of a few themes that I have used through the
years. While still a work in progress, and thus no CRAN release planned
for the moment, you can already try it out and see a collection of
themes: https://github.com/Bart6114/artyfarty.

library(ggplot2)
library(artyfarty)

ggplot(iris) +
  aes(x=Sepal.Length, y=Sepal.Width, color=Species) +
  geom_point() +
  scale_colour_manual(values = pal("flatpaleta")) +
  theme_flat() +
  ggtitle("Iris - sepal")

Or with a watermark:

ggplot(iris) +
  aes(x=Sepal.Length, y=Sepal.Width, color=Species) +
  watermark_img("flower.png") +
  geom_point() +
  scale_colour_manual(values = pal("flatpaleta")) +
  theme_flat() +
  ggtitle("Iris - sepal")