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switch variable: $colscale -- funct color scale
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switch value: 0 => RBG wheel1 (complex data)

This color scale designed for phase-encoded data
(e.g., retinotopic mapping).  With integral
angle_cycles (1,2,3), the scale is red->blu->grn
wrapping around at red.  With non-integral
angle_cycles there is only one red->blu->grn
cycle (phase values below red clampled to red and
phase values above green clamped to green).
