密度线之间的着色区域，根据相对位置

I have this plot

我有这个情节

set.seed(28100)
df <- data.frame(value = sample(1:10000,1000,replace=TRUE),
                 gender = sample(c("male","female"),1000,replace=TRUE))

ggplot(df, aes(value)) + 
  geom_density() +
  geom_density(data=subset(df, gender=='male'), aes(value), colour="blue") +
  geom_density(data=subset(df, gender=='female'), aes(value), colour="red")
set.seed(28100)
df