I've had several themes that I've tried on my BB Tour running OS 5.0.0.419 (and I've tried many of them on previous versions of the OS) that change all of the icons to the theme's icon set, except for certain icons, like my Gmail icon for example (I get Gmail using BIS). The icons for my other BIS accounts I have set up will change, but the Gmail one will not change. Can someone tell me why?
Gmail is not able to be changed when making a theme. There are a set amount of icons that we as developers are allowed to change- 3rd party apps are not one of them.
That is mostly true but there are some cases where it can be changed depending on how you want your theme to look. It is still not a user definable icon in any case.