Conditionally colored line plot

Plots (2D line) graph split into two colors above and below a given threshold value

Plots vectors x & y using one color for when y is greater than a given threshold value, and another color when y is less than the threshold.
You can optionally specify any standard formatting string that PLOT accepts (eg 'rx:' for a red dotted line with cross markers).

The plotting follows the standard MATLAB PLOT approach of linearly interpolating between data values. The coloring/linestyle changes at y = threshold, even on the interpolated line.