color scale

[Pam McDowell <pjmcdowell@xxxxxxxxxxxxxxx>]

I'm using the 'fill' and 'contour' options to plot temperature data. I
have defined a specific scale to consistently compare various data sets.
When a data set goes past the scale (either upper or lower value), no
color is plotted. How can I 'saturate' the colors at either end of the
scale. For example if a value is lower than my scale have it continue
with the lowest color (purple) or it the data exceeds the upper value
have 'fill' continue to plot highest color (red).