Add gradient colors to a bar chart with ggplot()

To emphasize value differences in a bar chart, using gradient colors is a nice option. ggplot makes it easy with scale_fill_gradient2().

Example

# create test data
col <- c('A', 'B', 'C', 'D', 'E')
val <- c(-4,  -2,  1,   3,  5)
df <- data.frame(col, val)

# create graph
ggplot(data = df, aes(x = col, y = val)) +
    geom_bar(stat = 'identity', aes(fill = val)) +
    scale_fill_gradient2(low='orange', mid='snow', high='blue')

low, mid and high values are from a list of Predefined Color Names.

Reference

RDocumentation