Silver Scratch on Apple Watch Series 4

I was using my Apple Watch regularly just sitting at a desk, and I look at it and see a silver scratch on the top right corner. My question is why is it silver? And is there a way to make it at least black again? I’ve tried rubbing it off but it seems stuck. When I rub my finger on it there is no texture showing that the glass is broken there. Is the glass cracked underneath? I’m not sure. Please explain