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switch variable: $colscale -- funct color scale
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switch value: 15 => MATLAB Jet (blu/cyan/yel/red)

The "jt" (MATLAB Jet) colorscale is for real data
(signed or all-positive), or for complex
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
(dark red, dark blue).  Negative numbers in
entries are OK as long as left entry smaller than
right.

Also in contrast to other color scales, extreme
values are dark, so well adapted to data with a
central tendency (light yellowish-green near
center of scale).

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 End Settings

When this color scale is interactively selected,
if only real data has previously been read onto
the surface, fmid and fthresh are set to 0.0 and
an initial estimate of the clamped ends of the
color scale (-5.0, 5.0) are set in the entries
under truncphase.  These can be subsequently
reset.

If data is real, $zerosymmfadeflag is set to 1
(fthresh/fmid and sfthresh/sfmid fade out data
symmetrically around zero).  If data is complex
(see next), $zerosymmfadeflag is set to 0 (to
display positive-only complex amplitude).

To toggle this flag on and off interactively,
click "Col:" to get the all-color-scales popup 
and do a *middle* click on "MATLAB Jet Signed".

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 clamp
the ends of the color scale to ($fthresh,
$fmid*4) and set $zerosymmfadeflag to 0.

To desaturate the colors, use small fslope (0.1)
with a negative fmid (-1.0).  This allows
background grays (or just gray if Col: "none" is
clicked) to begin to show through.

Flip Colorscale Ends

To flip ends of color scale use the "invphase"
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.
