Color difference
Calculate difference between two colors from 0 (same) to 100 (white/black).
Usage
var cd = require('color-difference');
cd.compare('#ffffff', '#ffffff'); // 0
cd.compare('#ffffff', '#000000'); // ~100.000
cd.compare('#ffffff', '#7f7f7f'); // ~46.807
cd.compare('#000000', '#808080'); // ~53.585
cd.compare('#7f7f7f', '#808080'); // ~0.392