It's pretty much confirmed that OS X 10.6 "Snow Leopard" will be darker. Just take a look at this screenshot of mobileMe and how dark the toolbar is. I bet Snow Leopard is gonna follow. So I guess this person I talked to was right.
I reached this conclusion because it's very coincidental that two sources imply dark interfaces and that Apple generally keeps similar interfaces among products.
And just another note: I've started the Wikipedia article Mac OS X v10.6.
Author of The Unix Geek and The Rambling World.
What I use:
MacBook (Early 2006) with Mac OS X 10.5.4
Dell Inspiron 530 with Windows Vista Ultimate and Ubuntu 8.04 Hardy Heron (dual-boot)
iPod nano 3rd generation, 4 GB silver