前端UI用的移动端的vantUI。这里只是我的思路总结，和用什么UI框架关系不大。
先看效果图：

    <van-calendar
      ref="calendar"
      :poppable="false"
      :show-confirm="false"
      :style="{ height: '580px' }"
      :min-date="minDate"
      :max-date="maxDate"
      :default-date="new Date()"
      :formatter="calendarFormatter"
      color="#dfdfdf"
    >
    </van-calendar>

this.dutyArray 在获取到所有的值班人员的时候，过滤好的，里面是没有重复的值班人

this.dutyArray.forEach((it) => {
  if (this.dutySet.indexOf(it.dutyPerson) == -1) {
     this.dutySet.push(it.dutyPerson);
   }
 });

重点来了！！！！

    calendarFormatter(day) {
      const month = day.date.getMonth() + 1;
      const date = (day.date.getDate() + "").padStart(2, "0");
      const year = day.date.getFullYear();
      const dateStr = `${year}-${month}-${date}`;
      // 当前day和dutyArray中的日期按顺序匹配，如果匹配上了，就显示值班人员
      const curDuty = this.dutyArray.find((it, idx) => {
        return it.dutyDate == dateStr;
      });
      if (curDuty) {
        day.bottomInfo = curDuty.dutyPerson;
      }

      // 判断当前的值班人，返回所在this.dutySet中的索引
      let index = this.dutySet.findIndex((it) => {
        return it == curDuty.dutyPerson;
      });
      if (index != -1) {
        if(index > 18){//防止溢出
          index = index % 18;
        }
        day.className = `cus-day-class${index}`;
      } else {
        day.className = `cus-day-class`;
      }
      return day;
    },

优雅实现css

<style lang="scss" scoped>
$colorArr: #1989fa, #6f7ad3, #f56c6c, #07c160, #e6a23c, #67c23a, #f06b49,
  #ecc2f1, #82c7c3, #e3698a, #d92b45, #60c9ff, #ba217d, #d2691e, #d2b48c,
  #ffa500, #ffc0cb, #ba55d3, #909399;

@each $colorItem in $colorArr {
  $index: index($colorArr, $colorItem);//当前索引
  .van-calendar
    ::v-deep
    .van-calendar__body
    .van-calendar__month
    .cus-day-class#{$index - 1}
    .van-calendar__bottom-info {
    background-color: $colorItem !important;
  }
}

</style>