echarts tooltip 自定义formatter怎么设置颜色？

1 formatter: function(params) {
2     var result = ‘‘;
3     params.forEach(function (item) {
4         result += ‘<span style="display:inline-block;margin-right:5px;border-radius:10px;width:9px;height:9px;background-color:‘ + item.color + ‘"></span>‘;
5     });
6 
7     return result;
8 }