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switch variable: $colscale -- funct color scale
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switch value: 7 => green/red (real data)

The rarely used "GR" (green-red) colorscale is
for signed, real-valued statistics.

Red is positive and green is negative (reversible
with revphaseflag).  Remains green and red as
significance increases.

Not affected by angle_offset, angle_cycles, and
invphase.
