A previous submission, confplot (by Michelle Giuliano) plots a single solid error boundary at one level of confidence. I just built on that idea by allowing the shade of the boundary to vary in a graded fashion across an array of confidence levels taken from a t distribution. If the confidence levels are spaced closely enough, e.g. [0.01:0.01:0.5], then the confidence boundary looks very smooth. You can use whatever color map you want to get all kinds of nice-looking effects.