SOLVED: YA book, paranormal, black-and-white dreams [s]

[rivka]

I read this one about 15 years ago, so it's at least that old.

Teenage girl meets up with teenage guy. They're having the same dreams, and they're in black and white (which turns out to be very significant). It all goes back to something that happened when their mothers were pregnant with them.

And I'm not sure, but I think there might be a roller coaster involved.

[rivka]

And thanks to Amazon's search-inside feature, I can confirm that it's definitely the right book.

Thanks! :)