thisFn = function() {
        delete parentContIn.coloraxis;
        delete parentContOut.coloraxis;
        return colorScaleDefaults(parentContIn, parentContOut, layout, coerce, opts);
    }
Colorscale / colorbar default handler

@param {object} parentContIn : user (input) parent container (e.g. trace or layout coloraxis object)
@param {object} parentContOut : full parent container
@param {object} layout : (full) layout object
@param {fn} coerce : Lib.coerce wrapper
@param {object} opts :
- prefix {string} : attr string prefix to colorscale container from parent root
- cLetter {string} : 'c or 'z' color letter