There are three editions of the S40 platform you can create themes for with Carbide UI,
3d Edition, 5th Edition and the newest one, 6th Edition.
When saving your Series 40 theme in Carbide UI, the tool offers different saving options:

Series 40 Theme v2.0 is meant for 3d Edition phones
Series 40 Theme v3.0 is for 5th and 6th Edition phones
Themes saved with the 2.0 option are installable on 3d, 5th and 6th Edition phones.
Themes saved with the 3.0 option are only installable on 5th and 6th Edition phones.
If you put a 2.0 theme on a 5th or 6th Edition phone, it will work but some of the elements (the ones that are only supported by 5th and 6th Edition phones) will remain in default state, no matter if you skinned them in Carbide UI or not.
There are six 240x320 6th Edition phones till now and their number will soon increase, so it might be interesting to know about the differences between themes put on 5th, resp. 6th Edition phones.
(The height difference between the 5th and 6th Edition screens is due to the 6th Edition emulator I took the screenshots from. It's 320x480 instead of 240x320.)
Here we go:
Different default icons
By default, 6th Edition phones show the new OVI icons.
Black statusbar gradient
On 6th edition phones, the statusbar icons are white instead of colourful. Additionally, there's now a permanent black gradient in the statusbar of all screens (except on the Idle Screen).
Scrollbar
When you skin the scrollbar in Carbide UI, the changes won't show up on 5th Edition phones. But they do on 6th Edition ones:

Active Idle Content Background
When activated, the semi-transparent AICB is black on 5th Edition phones. On 6th edition phones, it's white.

Digital Clock
On 5th Edition phones, assigning the digital clocks' colour wasn't supported. On 6th Edition phones, the digital clock will automatically take on the Idle Status Area Colour.

Dim Colour
When a popup appears, the submenue background is automatically dimmed black on 5th Edition phones. For 6th edition phones, you can now assign the dimming colour (example: pink) by selecting General > Dimming > Background Color in Carbide UI. When you don't skin it, it will be black.

Nested popups
On 6th Edition phones, some multiple-choice items aren't shown on the submenu background anymore. Instead they're shown on nested popups. (All popups can be skinned off the reel by changing Apps > Popup List > Popup List Background Display Main Highlight Layers in Carbide UI)

Skinning of List Highlight for unavailable items now supported
There are two separate list highlights, one for available and one for unavailable list items. Both can be skinned in Carbide UI*, but only the first one will appear on most 5th Edition phones while the latter one remains dark grey with a dark blue text. On 6th Edition phones, this bug has been fixed.
*Main Menu > List View > ...

Separate Tab Background not supported anymore
In Carbide UI, you can apply a separate background for the Tab View but you will only see it on 5th Edition phones. 6th Edition phones automatically use the Background Main image instead. However, the Tab Highlight is still supported.
