function updatePreview (ui) {
    try {
      const all = ui.val('all')
      activePreview.style.backgroundColor = (all && '#' + all.hex) || 'transparent'
      setAlpha.call(that, activePreview, (all && toFixedNumeric((all.a * 100) / 255, 4)) || 0)
    } catch (e) { /* empty fn */ }
  }
@param {external:jQuery} ui
@returns {void}