void ColorKeyN(values, intensity, nintensity, legllx, leglly, legurx, legury, labint, format, fontc, height, angle) COLORKEY.C Level 3
float *values The array of values at which the color used to represent the quantity of interest will change. This array must be in increasing order and is of dimension nintensity + 1.
int *intensity The intensity array is the list of the panel-filling colors that should be used to fill the cells. Order from lowest to highest. The dimension of this array is nintensity.
int nintensity The number of colors to be used in the legend.
float legllx, leglly, legurx, legury The lower-left and upper-right corners of the legend in inches (or cm).
int labint The color key will be labeled with the cell value every labint cells. If labint = 0, no labels will be used. If labint < 0, the maximum value of the label will not be plotted. (It may interfere with the next-to-last label.)
char *format The format string used to write the key labels. e.g., %-3.2f.
char fontc The font-selection character used for the color key labels.
float height The height of the color key labels in in (or cm).
int angle The angle of the color key labels in degrees measured clockwise from the x-direction.
ColorKeyN() is like ColorKeyL() except that the scale is arbitrary (nonlinear). This feature can be used to place more color levels in regions where the function varies slowly. 

The color key is placed in the region defined by the lower-left (legllx, leglly) and upper-right (legurx, legury) corners. Dimensions are in inches (or cm). The patterns will progress along the longest dimension of this rectangle. If the two corners are equal no legend will be drawn. Be sure to allow at least 1" width if labels are desired, and 1/2" if no labels are desired. Finally, you must plan to allow room for the color  key when you draw your axes.