I agree with Chris that it takes mille to make porcelains. As far as i know there are no real porcelain silkies. It's a mixture of colors people are calling porcelain.
The lighter one was closer to white, but definitely not white--unfortunately I lost her a couple of weeks ago or I could take her photo next to a white and you could see the difference.
Here are photos of the darker one with white and buff hens:
You can see lavender showing a bit in her wings and the undercolour of her head