JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" size="20" id="rbgTextbox" onkeypress="CheckKeyPress(event);" />

JavaScript

function CheckKeyPress(keyPressEvent) { 
        var element = document.getElementById('rbgTextbox');

         if (ValidateRGBTextboxInput(keyPressEvent)) 
             ChangeBackgroundColor(element.value); 
         else 
             return false;
    }

    function ValidateRGBTextboxInput(e) {
      return document.getElementById('rbgTextbox').value.length < 6 &&
       (e.which >= 48 &&
        e.which <= 57 ||
        e.which >= 65 &&
        e.which <= 70 ||
        e.which >= 97 &&
        e.which <= 102);
    }

    function ChangeBackgroundColor(color) {
        alert("Color is: " + color);
      //ById('gameArea').style.backgroundColor = '#'+color;
      //ById('nextPiece').style.backgroundColor = '#'+color;
    }