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switch variable: $colscale -- funct color scale
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switch value: 13 => color lookup table (complex ampl)

The "lta" (color lookup table, complex amplitude)
color scale is designed for user-entered
real-valued custom color look-up table for the
*amplitude* of a complex-valued signal.

Left-click the "Col:" label to get a popup to set
this scale, and R-click on the "lta" radio button
there for details on how to use this color scale.
