# Legend looks too dark to me, both onscreen and after printing to PDF
d = data.frame(x1 = 0:5, x2 = 5:10, x3 = 5:5, y1 = 0:0, y2 = 5:5, y3 = 10:10)
library(ggplot2)
ggplot(d) + theme_bw() +
    geom_ribbon(aes(x = x1, ymin = y1, ymax = y2, fill = 'red'),
                alpha = 0.5) +
    geom_ribbon(aes(x = x2, ymin = y2, ymax = y3, fill = 'red'),
                alpha = 0.5) +
    geom_ribbon(aes(x = x1, ymin = y2, ymax = y3, fill = 'blue'),
                alpha = 0.5) +
    geom_ribbon(aes(x = x2, ymin = y1, ymax = y2, fill = 'blue'),
                alpha = 0.5) +
    scale_fill_manual(name = NULL, values = c('red', 'blue')) +
    guides(fill = guide_legend(override.aes = list(alpha = 0.5)))
ggsave("p1.pdf", width = 6.5, height = 5)