Separate palettes for facets in ggplot facet_grid

Question

Question
How can I use a different color palette for each facet? Ideally I would like to have a generic legend in gray to serve as a reference.

Answer 1

faking a colour scale with transparency might be your best option, unless you're willing to combine multiple pieces at the grid/gtable level.

ggplot(diamonds) + 
  geom_bar(aes(x = clarity, stat = "bin", fill = cut, 
               alpha=arbitrary, group = arbitrary)) + 
  facet_grid(cut~.) + 
  scale_fill_manual(values = brewer.pal(name="Set1", n=5), guide="none") +
  scale_alpha_manual(values=c(0.8, 0.6, 0.4))