clplot( x, y, cutval, cols, varargin )

Creates a line plot whose color depends on which 'slice' of the y-range the y-value falls into.

clplot allows one to highlight the regions of a curve or dataset which fall into different ranges such as quantiles or critical performance levels. Unlike cheap imitations :-), clplot changes colors at exactly the range limits selected, rather than at the next actual data point. The latest version allows for multiple plots on the same graph.
Note: this is a clean, but not optimal implementation. See "clplot.r" in the Plotrix R-packagae for a better, but more complicated version (disclaimer: I wrote that as well).