const [r, g, b] = await extractColors(img);

// Let's say the LIGHTNESS_FACTOR is 0.4
const bgR = r * 0.4 + 255 * (1 - 0.4);
const bgG = g * 0.4 + 255 * (1 - 0.4);
const bgB = b * 0.4 + 255 * (1 - 0.4);

// This would return a color the same as if
// you were to apply an opacity of 0.4 to
// the original color and view it over a
// white background
return [bgR, bgG, bgB];