The dark bamboo is apparently heat treated which makes it softer.
Thanks for the info about the Janka rating. You can order some samples very cheaply from eBay, so I'll order some laminate ones and do a scratch test. The online articles I read from people with (large) indoor dogs, seem to agree on the laminate as a cheap and easy to maintain alternative to wood. And laminate gets an AC (Abrasion Class) rating, which seems more useful than the Janka rating. I'd like to get the commercial grade AC4 stuff, but may have to settle for the AC3, which is easier to find.
Now I just have to wait for my bonus at work before I go searching for the best deal! But I'll call around for some quotes in the mean time.
While the foster pup amuses herself with pulling threads out of the carpet when she's bored... Haha!