html.（用于显示颜色）

  <div style=" width: 200px;height: 200px"></div>

JS.

function getcolor(){     //获取随机色（#ffffff格式）
            let sljz=["0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"]
            let str="#"
            for(let i=0;i<6;i++){     //用for循环6次将16进制数加到arr里去（形成6位数）
                 let a=Math.floor(Math.random()*16)      //生成0~15的随机数
                 str+=sljz[a] 
            }
                 return str      //返回#ffffff格式随机色
            }
     const div=document.querySelector("div")
     div.style.background=getcolor()    //div获取随机颜色

页面效果（每刷新一次页面，div随机上色）