Shade region between two lines with ggplot

How about using geom_ribbon instead

ggplot(x, aes(x=x, y=twox)) +     geom_line(aes(y = twox)) +     geom_line(aes(y = x2)) +    geom_ribbon(data=subset(x, 2 <= x & x <= 3),           aes(ymin=twox,ymax=x2), fill="blue", alpha=0.5) +    scale_y_continuous(expand = c(0, 0), limits=c(0,20)) +    scale_x_continuous(expand = c(0, 0), limits=c(0,5)) +     scale_fill_manual(values=c(clear,blue))

I think that geom_ribbon is the way to go. There are 2 steps to go:

1. Data Manipulation: You should manipulate data to define ymin & ymax for arguments in geom_ribbon
2. Draw plot with geom_ribbon.

Let's see my example:

#Data library(gcookbook) # Data Manipulationcb <-subset(climate,Source=="Berkeley")cb$valence[cb$Anomaly10y >= 0.3] <- "pos"cb$valence[cb$Anomaly10y < 0.3]  <- "neg"cb$min <- ifelse(cb$Anomaly10y >= 0.3, 0.3, cb$Anomaly10y)cb$max <- ifelse(cb$Anomaly10y >= 0.3, cb$Anomaly10y, 0.3)#Drawing plotggplot(cb,aes(x=Year,y=Anomaly10y)) +geom_ribbon(aes(ymin = min, ymax = max, fill = valence), alpha = 0.75) +scale_fill_manual(values = c("blue", "orange")) +geom_line(aes(col = valence), size = 1) +scale_color_manual(values = c("blue", "orange")) +geom_hline(yintercept=0.3, col = "blue") +theme_bw()