Ok, I found some time to take a look at this and adding this to my .emacs fixes the issue:
(defadvice vm-show-current-message (after u-vm-color activate) (u-vm-color-fontify-buffer-even-more))
The earlier advice for "vm-decode-mime-message" was not being invoked for us-ascii messages, which is why the fontification wasn't being done.
Ok, I found some time to take a look at this and adding this to my .emacs fixes the issue:
(defadvice vm-show- current- message (after u-vm-color activate) color-fontify- buffer- even-more) )
(u-vm-
The earlier advice for "vm-decode- mime-message" was not being invoked for us-ascii messages, which is why
the fontification wasn't being done.