I've been doing quite a bit of experimenting with the themes in this (and other versions).
It seems that this version does not require the removing of the net_rim_theme_tmobile_BlackBerry6_480x360_b.cod file in order to not get the black/white no-theme problem.
I tried the net_rim_theme_tmobile_BlackBerry6_480x360_b.cod from several different versions of OS6 for the 9700, including .344, and .358 and both of those had issues when loaded on the 9700 and 9780. They don't load properly and require the removal of it in order to get a theme to load on the device.
I'm not sure if it's a problem with the theme file itself or a conflict with another file like the main BlackBerr6 theme cod file. However, the TMobile, and other carrier theme files are not really full themes. They simply label the BlackBerry6 theme file as "BlackBerry 6 for TMobile" instead of just a basic "BlackBerry 6" theme. It's only around 100KB in size.
So far, on the 9700 the .380 TMobile theme file is the only one that works properly The only other theme that works properly is the TMobile theme file from the 9780 v184.108.40.2065 that is shipping on the TMobile US 9780 device.
If you want to try that theme file you can get it with the 9780 OS for TMobile. You can download it here: FileDownload