shading plots by confidence/variance

[afredston]

Hi all! I know I've seen R-generated plots (particularly maps) before with a base color ramp that corresponds to values, and then some form of shading or other overlay on top of that color ramp that indicates confidence or variability in the results (lower confidence = paler, crosshatched, etc.). Someone asked me to help them do this in R, and I can't find any papers with this type of figure, although I know I've seen some. Has anyone else seen this type of plot, or R vignettes that demonstrate how to do this?