Changes have been made in Git for this ticket:

All embedded information now lives under the original part.
Resolves Ticket #8296; Ticket #8629

Don't replace the original part with the embedded information. This
ensures we can always uniquely access the original data if necessary.
Also allows us an easier method to show status messages for related data
and allows us to do fancier things like wrapping entire parts with
colored borders (i.e. multipart/encrypted, multipart/signed).

Fixes problems with S/MIME encrypted/signed messages.

http://git.horde.org/diff.php/imp/docs/CHANGES?rt=horde-git&r1=7e7c28dd6bf2f2078b9e2efa66041a0c22babc8a&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Contents.php?rt=horde-git&r1=b879fbf80e084ac1d43d439083a5da0a35f01419&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Partial.php?rt=horde-git&r1=b879fbf80e084ac1d43d439083a5da0a35f01419&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Pgp.php?rt=horde-git&r1=ba9857f21277a77d8f243638bd433a33ae4b2255&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Plain.php?rt=horde-git&r1=71466fedc7a8c82a1a7157ccb637749e7f4700c1&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Smime.php?rt=horde-git&r1=b879fbf80e084ac1d43d439083a5da0a35f01419&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/themes/screen.css?rt=horde-git&r1=c3733d574889dbade4b7f2535f823a068b21d970&r2=2faf375710fbfb550f993776203eb2b1df57395d

Changes have been made in Git for this ticket:

All embedded information now lives under the original part.
Resolves Ticket #8296; Ticket #8629

Don't replace the original part with the embedded information. This
ensures we can always uniquely access the original data if necessary.
Also allows us an easier method to show status messages for related data
and allows us to do fancier things like wrapping entire parts with
colored borders (i.e. multipart/encrypted, multipart/signed).

Fixes problems with S/MIME encrypted/signed messages.

http://git.horde.org/diff.php/imp/docs/CHANGES?rt=horde-hatchery&r1=7e7c28dd6bf2f2078b9e2efa66041a0c22babc8a&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Contents.php?rt=horde-hatchery&r1=b879fbf80e084ac1d43d439083a5da0a35f01419&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Partial.php?rt=horde-hatchery&r1=b879fbf80e084ac1d43d439083a5da0a35f01419&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Pgp.php?rt=horde-hatchery&r1=ba9857f21277a77d8f243638bd433a33ae4b2255&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Plain.php?rt=horde-hatchery&r1=71466fedc7a8c82a1a7157ccb637749e7f4700c1&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/lib/Mime/Viewer/Smime.php?rt=horde-hatchery&r1=b879fbf80e084ac1d43d439083a5da0a35f01419&r2=2faf375710fbfb550f993776203eb2b1df57395d
http://git.horde.org/diff.php/imp/themes/screen.css?rt=horde-hatchery&r1=c3733d574889dbade4b7f2535f823a068b21d970&r2=2faf375710fbfb550f993776203eb2b1df57395d

This should be easy enough to fix/hack around - the verifying code 
could easily store the information in the parent multipart/signed 
Viewer and/or part so that all other children parts can access this 
information.
I assume you are talking about the "fake" parts created from the 
armored text.  That was a rough first implementation (my personal 
motiviation to play around with armored messages is limited because it 
was deprecated ages ago) but a necessary one since armored messages 
may contain multiple parts inside of them.  Display of the 'x-imp...' 
part is best hidden at some point in the future (the part is currently 
necessary because it is the only place that contains the full text of 
the message necessary to verify the signature).

Yes, I already got that far, but the problem is that the mime parts 
responsible for verifying the signature (and providing the bg color) 
and for rendering the actual message text (and showing the bg color) 
don't "know" of each other. Thing especially get worse if re-building 
a "virtual" message from embedded mime parts if the message is inline 
armored.

Btw, in this case, the part information being displayed in the message 
view is incorrect because it reflects the virtual message, not the 
original one.

In git this could easily be done but slightly modifying the return 
from Horde_Mime_Viewer::render().  At one point, I believe I had added 
a 'bg' item - I think I took it out because we weren't using it 
anywhere.  Just would need to re-add this.  Then, when looping through 
the render code (in message.php and lib/Views/ShowMessage.php), the 
classname information would be available in the return from 
IMP_Contents::renderMIMEPart() and could easily be added to the 
mimePartInfo SPAN element.

This simple patch adds some really nice background highlighting to 
signed PGP messages. Good messages get a green background, bad 
messages a red one.

Unfortunately it's next to impossible to port this to Git with the 
current code layout, since the verification result is stored in a mime 
part distinct from the actual message. Any ideas how to get this 
working in Git are welcome.