HTML CSS
(a quick guide)
CSS TRANSITION #demo { background: red; transition: background-color 1s; }
<div id="demoA">HOVER</div>
CHANGE COLOR ON HOVER #demo:hover { background: green; }
KEYFRAMES COLOR SEQUENCE @keyframes rgb { 0% { background-color: red; } 50% { background-color: green; } 100% { background-color: blue; } }
ATTACH KEYFRAMES TO ELEMENT #demoB { animation: rgb 3s infinite alternate; }
<div id="demoB">RGB</div>