Here is some invented data and a plot that is similar to yours with the shaded region in a bluish color. If the call to ggplot does not help you, perhaps you can use the data as part of your reprex.
#Inventing data
vec <- sin(seq(from = 0, to = 2 * pi, by = 0.02 * pi))
vecPlus <- vec + runif(length(vec), min = 1, max = 2)
vecMinus <- vec - runif(length(vec), min = 1, max = 2)
DF <- data.frame(X = seq(from = 0, to = 2 * pi, by = 0.02 * pi), vec, vecPlus, vecMinus)
#Plotting
library(ggplot2)
ggplot(DF, aes(x = X, y = vec, ymin = vecMinus, ymax = vecPlus)) +
geom_line(color = "red", size = 2) +
geom_ribbon(fill = "skyblue", alpha = 0.5) +
theme_classic()

Created on 2020-05-27 by the reprex package (v0.3.0)