Dear
In the current released version (4.0SP1) you can change the SAP logo easily (NWBC_CFG table) and there is the new landing page (lanes page) available with Renewal 1.0 SP3 which supports a background image which is what you see for the HR Management landing page in all the demos, but I don't believe you can set a different background apart from this page with the current version. Well, at least not via supported methods at the moment. I also haven't come across any colour personalisation in my travels yet which is probably a future release feature I'm guessing.
That's just my understanding though, and will leave it up to the NWBC product guys to let you know for sure.
Regards