What's the Name of That Book??? discussion

I read this book about 2004 or 2005. It was a fantasy novel, the heroine was a young woman in a fictional world. She had birthmarks all over her body that were a design. They were getting darker, more intricate. She was hiding the designs from everyone. I THINK other people with the same designs were dying and she was trying to figure out why? At one point she goes to a castle/palace to find out more information, and there are trees growing inside the entryway. I believe she had a brother or lover who had the designs also.

I thought the book had "dark" in the title, but I can't find it.

Sounds similar to Cast in Shadow. Is this it?

Yes! Well done! And so quickly. Thank you!

Glad to have helped :) enjoy!