Save off at least one attribute data array.

Not saving off all point and cell and field arrays yet, for the moment
I'm choosing just one point associated array.

Not sure which of several possible places in the geojson is correct for
this. Could be supplemental to x,y,z as here, or in a separate member of
the geometry, or in the features properties. This works for our purposes.

Note I am doing the LUT translation to color space here. Ideally we will
instead keep the data as is and let the consumer handle that.