colorFade.js

var colorStops = [
  { p: 0.1, c: [244, 67, 54] },
  { p: 0.5, c: [255, 236, 59] },
  { p: 1.0, c: [76, 175, 79] }
];

var getColorForPercentage = function (p, stops) {
  p = (p < 0) ? 0 : (p > 1) ? 1 : p;
  for (var i = 1; i < stops.length - 1; i++) {
    if (p < stops[i].p) {
      break;
    }
  }
  var l = stops[i - 1];
  var u = stops[i];
  var r = u.p - l.p;
  var rp = (p - l.p) / r;
  return [
    Math.floor(l.c[0] * (1 - rp) + u.c[0] * rp),
    Math.floor(l.c[1] * (1 - rp) + u.c[1] * rp),
    Math.floor(l.c[2] * (1 - rp) + u.c[2] * rp)
  ];
}