Vita C serum turns pink?

Normally I put my skincare in my cabinet. And few days ago I found this serum turns to pink. I received this serum two months ago and I directly use it as it is PR. At that time the texture is white. Then I put it in my skincare cabinet and use it differently with my other serum. Mean I don't use it everyday. Now the texture turns pink, it is spoilt or oxidize? Can I use it on my face?