if first time I want to select or changing the radio button I want to change the label color to red, but it not working perfectly, I use a on change function inside radio button
<script>
function changecolor(){
document.getElementsByClassName("label").style.color='red'
}
</script>
<body>
<div class="group">
<label for="one" class="label">Select Any</label>
<div class="input">
<input id="one" class="radio" name="radio-group" type="radio" onchange="changecolor()" >
<input id="one" class="radio" name="radio-group" type="radio" onchange="changecolor()">
</div>
</div>
</body>
</html>
document.getElementsByClassName return an htmlcollection so you have two solutions to make work your code
function changecolor(){
document.getElementsByClassName("label")[0].style.color='red'
}<div class="group">
<label for="one" class="label">Select Any</label>
<div class="input">
<input id="one" class="radio" name="radio-group" type="radio" onchange="changecolor()" >
<input id="one" class="radio" name="radio-group" type="radio" onchange="changecolor()">
</div>
</div>