This is largely by Rosemary Stanley codepen.io/mrsdohpaz/pen/PPWVyZ)

This uses animation with keyframes set to a gradient of colors changing every 10%.

background-image: linear-gradient( rgba(255, 255, 255, 0.5), rgba(0, 0, 0, 0.6));
background-color: #FFFA02;
animation: rgb 30s infinite alternate;
@keyframes rgb { 10% { background-color: #FF6B02; }