public float diff(MultiColor b)
        {
            float res = 0;
            for (int i = 0; i < data.length; i++)
            {
                if (data[i] == -1 || b.data[i] == -1)
                    continue;

                float d = data[i] - b.data[i];
                res += d * d;
            }
            return res;
        }