调用该方法则会返回一个#xxx的rgb随机颜色
function color1(){
var sum="";
var shuzu2=['a','b','c','d','e','f','0','1','2','3','4','5','6','7','8','9'];
for(var i=1;i<=3;i++){
var int2=parseInt(Math.random()*shuzu2.length); //生成随机下标
sum+=shuzu2[int2]; //将该下标所对应的值保存
}
var sum2="#"+sum; //将值字符串连然后保存
sum="";
return sum2;
}