Help System (web edition)

Both in PLOT and GPLOT also negative values -1,-2,... may be used
in the SHADING list. Each negative value -n correspond to a specific
color which must be defined by a FILL specification of the form
FILL(-n)=c,m,y,k where c,m,y,k are numbers on the interval (0,1) and
give the color components according to the CMYK (Cyan, Magenta, Yellow,
blacK) system. These values are used as such in PostScript but in GPLOT
they are converted into the RGB (Red,Green,Blue) system.

Use of COLOR(n) specifications is recommended instead of FILL(-n).

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This example shows how the shading values 2,3,4 (when color98=0)
are close to selected negative values -1,-2,-3:
GPLOT RGB / Activate this command!
DATA RGB
N R1 R2 G1 G2 B1 B2
A 1  1  1  1  1  1

SHADING=2,-1,3,-2,4,-3  GAP=0 C98=0
FILL(-1)=0,1,1,0.3
FILL(-2)=1,0,1,0.3
FILL(-3)=1,1,0,0.3
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Negative shading values should be preferred especially in cases where
the final plotting is to be done by PLOT (PostScript).
The CMYK colors in PostScript may slightly differ from those used in
GPLOT depending on the device used for PostScript plotting.
Usually a small adjustment in the last CMYK component (Black) will
improve the correspondence.

  S = More information on SHADING