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switch variable: $colscale -- funct color scale
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switch value: 16 => MBCGYR wheel (complex data)

The "w3" (wheel3) color scale is designed for
phase-encoded data.  The scale is:

  Magenta->Blue->Cyan->Green->Yellow->Red

followed by a mirror image of that sequence:

  Red->Yellow->Green->Cyan->Blue->Magenta

This color scale is specific to polar angle data.
A quarter cycle offset is included so that zero
phase corresponds to the horizontal meridian.

The scale can be rotated by using $angle_offset.
Using $truncphaseflag works, but $angle_cycles
and $invphaseflag have no effect.
