You can use the following basic syntax to change the color of bars in a stacked bar chart in ggplot2:

#create stacked bar chart
ggplot(df, aes(x=x_var, y=y_var, fill=fill_var)) + 
  geom_bar(position='stack', stat='identity') +
  scale_fill_manual(values=c('red', 'purple', 'pink', ...))

The following example shows how to use this syntax in practice.

Example: Change Color of Bars in Stacked Bar Chart in ggplot2

Suppose we have the following data frame in R that shows the points scored by various basketball players:

#create data frame
df <- data.frame(team=c('A', 'A', 'A', 'B', 'B', 'B', 'C', 'C', 'C'),
                 position=c('G', 'F', 'C', 'G', 'F', 'C', 'G', 'F', 'C'),
                 points=c(22, 12, 10, 30, 12, 17, 28, 23, 20))

#view data frame
df

  team position points
1    A        G     22
2    A        F     12
3    A        C     10
4    B        G     30
5    B        F     12
6    B        C     17
7    C        G     28
8    C        F     23
9    C        C     20

If we create a stacked bar chart to visualize the points scored by players on each team, ggplot2 will use a set of to fill in the bars:

library(ggplot2)

#create stacked bar chart
ggplot(df, aes(x=team, y=points, fill=position)) + 
  geom_bar(position='stack', stat='identity')

However, we can use the scale_fill_manual() argument to specify the exact colors that ggplot2 should use for the bars:

library(ggplot2)

#create stacked bar chart with custom colors
ggplot(df, aes(x=team, y=points, fill=position)) + 
  geom_bar(position='stack', stat='identity') +
  scale_fill_manual(values=c('red', 'purple', 'pink'))

The bars now have the exact colors (in order from top to bottom) that we specified within the scale_fill_manual() function.

Also note that we can use hex color codes within the scale_fill_manual() function:

library(ggplot2)

#create stacked bar chart with custom hex color codes
ggplot(df, aes(x=team, y=points, fill=position)) + 
  geom_bar(position='stack', stat='identity') +
  scale_fill_manual(values=c('#2596BE', '#8225BE', '#D4C443'))

The bars now have the hex color codes that we specified.

The following tutorials explain how to perform other common tasks in ggplot2: