colorChanged = (elem) => {
      const color = elem.getAttribute('stroke')

      mtypes.forEach((pos) => {
        const marker = getLinked(elem, 'marker-' + pos)
        if (!marker) { return }
        if (!marker.attributes.se_type) { return } // not created by this extension
        const ch = marker.lastElementChild
        if (!ch) { return }
        const curfill = ch.getAttribute('fill')
        const curstroke = ch.getAttribute('stroke')
        if (curfill && curfill !== 'none') { ch.setAttribute('fill', color) }
        if (curstroke && curstroke !== 'none') { ch.setAttribute('stroke', color) }
      })
    }
Called when the main system modifies an object. This routine changes
  the associated markers to be the same color.
@param {Element} elem
@returns {void}