[R] How to add legend to 2 different data frame overplot?

[C W]

Hi,

I am trying to do add a legend to an overplot, something like this:

ggplot() +
    geom_density(data = df1, aes(x = x), fill = "green", show_guide =
FALSE) +
    geom_area(data = df2, aes(x = x), fill = "yellow", show_guide = FALSE) +
    scale_color_manual(values = c("green", "yellow"), labels = c('df1',
'df2'))

But the legend doesn't actually show up when I plot it.  How should I fix
this?

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