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.
Confirmed: OS X Snow Leopard Will Be Darker
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.