Using setInterval in javascript

I modified a javascript code using setInterval to alternate between two messages using innerHTML. I tried document.write and it works. But innerHTML does not work.

// Create global interval and color variables
let interval;
let sentence;
let word;
let color = 'white';
// const word = document.querySelector("#one").innerHTML;
function startTogglingBg() {
  word = document.querySelector("#one").innerHTML;
  interval = setInterval(function() {
    if (color === 'white') {
      sentence = "Hey";
      color = 'red';
    } else {
      sentence = "You!";
      color = 'white';
    }
    // document.body.style.backgroundColor=color;
    // document.write(sentence);
    word = sentence;
  }, 1500);
}

function stopTogglingBg() {
  clearInterval(interval);
}

window.addEventListener('load', function() {
  btnStart = document.getElementById('start');
  btnStop = document.getElementById('stop');

  btnStart.addEventListener('click', startTogglingBg);
  btnStop.addEventListener('click', stopTogglingBg);
});
<button id="start">Start</button>
<button id="stop">Stop</button>

<p id = "one">Hello</p>

I expected the p tag value will change from the words “Hey” and “You!” every 1.5 seconds using setInterval. I tried document.write and it worked but the result is like this:

HeyYou!HeyYou!HeyYou!.......