An update to the first solution here: https://gist.github.com/jayzawrotny/3079b17004a5237910a58f877bac1d58f

color-graduation.js

// Vanilla solution
let format = require('util').format;

const COLORS = [
  { stop: 0, rgb: [35, 198, 161] },
  { stop: 6, rgb: [245, 235, 73] },
  { stop: 48, rgb: [245, 51, 0] },
];

function getRGBColor (hours) {
  // ordering of max and min IS IMPORTANT as we're mutating the colors array with reverse
  let colors = COLORS.slice(0),
      min = colors.reduce((min, color) => color.stop <= hours ? color : min),
      max = colors.reverse().reduce((max, color) => color.stop >= hours ? color : max), 
      normalizationFactor;

  // control for out of bounds, use the same value twice in such an event
  max = max || min;
  min = min || max;

  // calculate the normalization factor, should always be between 0 - 1
  normalizationFactor = (hours - min.stop) / (max.stop - min.stop);

  // at this point we don't care about the stops anymore, just the rgb and factor
  // calculate and return one RGB array
  return min.rgb.map((c, i) => {
    let rgb1 = min.rgb[i],
        rgb2 = max.rgb[i],
        normalizedDiff = (rgb2 - rgb1) * normalizationFactor,

    return Math.round(rgb1 + normalizedDiff);
  });
}

// Timer logic
// Pretty shitty but just playing around
function simulateTime () {
  const NOW = Date.now();
  const eventDate = NOW + (1000 * 60 * 60 * 24 * 2); // 2 days from now

  let currentTime = NOW;

  let interval = setInterval(() => {
    if (currentTime < eventDate) {
      let duration = eventDate - currentTime,
          hours = Math.ceil(duration / 1000 / 60 / 60),
          color = getRGBColor(hours);

      console.log(`${format(color)} ${new Date(currentTime).toString()} ${hours} hours before the event`);

      currentTime += 1000 * 60 * 60 * 2; // increment by 2 hours
    }
    else if (currentTime >= eventDate + 3000) {
      clearInterval(interval);
    }
  }, 1000);
}

simulateTime();