I don't even have a'n' N900 and I still see the usefulness of the offer made here. If you don't want to, then I will.

Such as, the default wallpaper could be "." Without the health bars in the corner. As long as we get the infamous crowbar and black mesa logo.
Or a random picture of G-Man would suffice.

Also, the device beginning song could be "Half- Life Theme Song". Can't get any better than that.

From the video, you can see the logo shades from red to orange hue. Also from light grey to dark grey. Those could be the underlying colours to the theme. Gives a lot of colours to experiment with, unlike the one colour orange of the Mesa logo which might not work well with people. (By the way, that mesa logo on the video will work really well with this theme when it does get created.)

Why am I doing this, an opportunity presented itself here to remember forever the "1" game of all time.

Long live the N800, and "LONG LIVE THE G-MAN!"

P.S. If you don't mind, an N800 theme would be very very much welcomed and appreciated if time permits.