how to change input border color with js

 var getColor = prompt("Choose your color ", "Enter the  color ");
 var color;
 var el = document.getElementById("color");
 el.innerHTML = "Whatever paragraph message.";
 if (getColor =="Yellow" || getColor =="yellow" || getColor =="YELLOW"){
     color = "#FFFF66";
     el.style.borderColor = color;
 } 
.borders{
    background-color:#00ffff;
    border-color:#000000;
    border-width:2px;
    border-style:solid;
}document.getElementById("fName").className = document.getElementById("fName").className + " error";  // this adds the error class

document.getElementById("fName").className = document.getElementById("fName").className.replace(" error", ""); // this removes the error class