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switch variable: $colscale -- funct color scale
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switch value: 17 => CARET "videen-style" (spectral)

The "vd" (CARET "videen-style" spectral) color
scale is for real data (signed or all positive),
or for complex data amplitude.

N.B.: unlike other colscales, to control this
color scale, enter bottom and top data values
into the unmarked entries under the truncphase
button enter data values.  Any data values
smaller than the left entry or larger than the
right entry are clamped to the limiting colors
(black, red).  Negative numbers in entries are OK
as long as left entry smaller than right.

Fade-out Options

Color is truncated to background when the
real-valued data below $fthresh (and/or fades out
below $fmid, which sets 50% saturation point).

If a stat has also been loaded (and "mask"
ticked), colors are also truncated to background
when the *stat* is below $sfthresh (and/or fades
below $sfmid, which sets 50% saturation point).

The setting of $zerosymmfadeflag (see next)
determines whether fthresh/fmid and 
sfthresh/sfmid threshold data from the bottom, or
whether they cut into data symmetrically around
zero.

For full color saturation, set fthresh and fmid
to 0.0.

Initial Scale Settings

When this color scale is interactively selected,
$zerosymmfadeflag is set to 0.  To toggle this
flag on and off interactively, click "Col:" to
get the all-color-scales popup and do a *middle*
click on "CARET Videen-Style".  If set,
fthresh/fmid and sfthresh/sfmid fade out data
symmetrically around zero.

Complex Data (amplitude)

If complex-valued data has previously been read
onto the surface, then the complex amplitude will
be colored.  This will instead initially auto-set
$fthresh to 0, and clamp ends of the color scale
to (0.0, $fmid*4).

Flip Colorscale

To flip ends of color scale use the "invph"
tickbox ($invphaseflag is 1).  This flips around
zero, so you will have to adjust the color scale
ends if they are not symmetric around zero.
