multi-color-labels.R

# Load data and create base plot
mtcars$names <- rownames(mtcars)
p <- ggplot(mtcars, aes(x=wt, y=mpg)) +
  geom_point(aes(size = disp, color = as.factor(carb))) +
  scale_color_brewer(palette="Set1") +
  scale_size(range=c(1,20)) +
  scale_x_continuous(limits=c(1,4.5)) +
  theme_minimal() +
  theme(legend.position = "none")

# Single color labelling with unsatisfactory contrast
p + geom_text(data = mtcars %>% filter(mtcars$disp > 380), aes(label=names), hjust=0)

firebird <- mtcars[mtcars$names == "Pontiac Firebird",]

# Simple over-printing for improved contrast
p + 
  annotate("text", x = firebird$wt, y=firebird$mpg, hjust = 0,
           label="Pontiac Firebird", color="black") +
  annotate("text", x = firebird$wt, y=firebird$mpg, hjust = 0,
           label="Pon", color="white")

# Elaborate over-printing for improved contrast
p + 
  annotate("text", x = firebird$wt, y=firebird$mpg, hjust = 0, parse=T,
           label='"Pon" * phantom("tiac Firebird")', color="white") +
  annotate("text", x = firebird$wt, y=firebird$mpg, hjust = 0, parse=T,
           label='phantom("Pon") * "tiac Firebird"', color="black")