These aesthetics parameters change the colour (colour and fill) and the opacity (alpha) of geom elements on a plot. Almost every geom has either colour or fill (or both), as well as can have their alpha modified. Modifying colour on a plot is a useful way to enhance the presentation of data, often especially when a plot graphs more than two variables.

Colour and fill

Colours and fills can be specified in the following ways:

  • A name, e.g., "red". R has 657 built-in named colours, which can be listed with grDevices::colors().

  • An rgb specification, with a string of the form "#RRGGBB" where each of the pairs RR, GG, BB consists of two hexadecimal digits giving a value in the range 00 to FF. You can optionally make the colour transparent by using the form "#RRGGBBAA".

  • An NA, for a completely transparent colour.


Alpha refers to the opacity of a geom. Values of alpha range from 0 to 1, with lower values corresponding to more transparent colors.

Alpha can additionally be modified through the colour or fill aesthetic if either aesthetic provides color values using an rgb specification ("#RRGGBBAA"), where AA refers to transparency values.

See also


# \donttest{ # Bar chart example p <- ggplot(mtcars, aes(factor(cyl))) # Default plotting p + geom_bar()
# To change the interior colouring use fill aesthetic p + geom_bar(fill = "red")
# Compare with the colour aesthetic which changes just the bar outline p + geom_bar(colour = "red")
# Combining both, you can see the changes more clearly p + geom_bar(fill = "white", colour = "red")
# Both colour and fill can take an rgb specification. p + geom_bar(fill = "#00abff")
# Use NA for a completely transparent colour. p + geom_bar(fill = NA, colour = "#00abff")
# Colouring scales differ depending on whether a discrete or # continuous variable is being mapped. For example, when mapping # fill to a factor variable, a discrete colour scale is used. ggplot(mtcars, aes(factor(cyl), fill = factor(vs))) + geom_bar()
# When mapping fill to continuous variable a continuous colour # scale is used. ggplot(faithfuld, aes(waiting, eruptions)) + geom_raster(aes(fill = density))
# Some geoms only use the colour aesthetic but not the fill # aesthetic (e.g. geom_point() or geom_line()). p <- ggplot(economics, aes(x = date, y = unemploy)) p + geom_line()
p + geom_line(colour = "green")
p + geom_point(colour = "red")
# For large datasets with overplotting the alpha # aesthetic will make the points more transparent. df <- data.frame(x = rnorm(5000), y = rnorm(5000)) p <- ggplot(df, aes(x,y)) p + geom_point()
p + geom_point(alpha = 0.5)
p + geom_point(alpha = 1/10)
# Alpha can also be used to add shading. p <- ggplot(economics, aes(x = date, y = unemploy)) + geom_line() p
yrng <- range(economics$unemploy) p <- p + geom_rect(aes(NULL, NULL, xmin = start, xmax = end, fill = party), ymin = yrng[1], ymax = yrng[2], data = presidential) p
p + scale_fill_manual(values = alpha(c("blue", "red"), .3))
# }