I thought the serum has gone bad because the color was weird but then I found these photos on Taobao:
Damn, I thought it had gone bad back then and threw it away. But the color of the C15 is just like that from the beginning as it seems.
"We are grinding the MAP a bit differently which gives it a hazy appearance but the result is that it is very silky and smoother and feels great when applied. It absorbs more effectively too. There is no change in the formula -- it's just the shape and size of the MAP crystals are improved that causes the hazy look.One thing about the hazy appearance of the CelSignal from our making it silkier -- it does clear up in about 5 days once opened. This depends on temperature."
I kind of miss that serum because it was so gentle. And it has 10% niacinamide. Even niacinamide serums usually contain only 5 percent. A lot of Korean whitening products contain niacinamide, but again it is below 5 percent. Other serums with 7 or more percent are crazily expensive!