javascript能改变body的背景颜色怎么不能改变父元素的相邻元素的背景颜色

问题遇到的现象和发生背景
问题相关代码,请勿粘贴截图
<!DOCTYPE=html>
    <html lang="zh-cn">

    <head>
        <meta charset="UTF-8">
        <title>
            关于文档元素测试
        </title>
        <style>

            .son1 {

                height: 30px;
                width: 100px;
                background-color: orange;
            }

            .son2 {

                height: 30px;
                width: 100px;
                background-color: red;
            }

            .son3 {
                height: 30px;
                width: 100px;
                background-color: #08a9b5;
            }


            .son4 {
                height: 30px;
                width: 100px;
                background-color: #9ad1c3;
            }

            .son5 {

                height: 30px;
                width: 100px;
                background-color: rgb(21, 123, 126);
            }
            .grand_father{
                display: inline-block;
            }
            .mother{
                box-sizing: border-box;
                width: 100%;
                height: 250px;
                margin-top: 5px;
                border: 1px solid black;
                background-color: orange;
            }
            body{
                display: flex;
                justify-content: center;
                align-items: center;
            }
        </style>
    </head>

    <body>
        <div class="grand_father">
            <div class="father">
                <button class="son1">q</button>
                <button class="son2">w</button>
                <button class="son3">e</button>
                <button class="son4">e</button>
                <button class="son5">e</button>
            </div>
            <div class="mother">
            </div>
        </div>
        <script>
            var father = document.querySelector('.father');
            var sons=father.querySelectorAll('button');
            // console.log(sons);
            for(var i=0;i<sons.length;i++ ){
                sons[i].my_index=i;
                sons[i].onclick=function(){
                    var ind=this.my_index;
                    var son_obj=window.getComputedStyle(sons[ind]);
                    var son_obj_color=son_obj.backgroundColor;
                    // document.body.style.backgroundColor= son_obj_color;
                    var mother = document.querySelector('.mother');
                    var mother_obj = window.getComputedStyle(mother);
                    var mother_obj_color = mother_obj.backgroundColor;
                    mother_obj.backgroundColor=son_obj_color;
                    // console.log(mother_obj_color);

                }
            }
        </script>
    </body>

    </html>

运行结果及报错内容
我的解答思路和尝试过的方法
我想要达到的结果

你是想实现说,点击上面的按钮,然后下面的盒子颜色跟按钮一样的颜色吗