We've been experiencing this issue since upgrading to GroupWise 7; we're now operating in 7.02. One of our end users has a default compose and reply font that was changed to TNR blue, even though his default font is set to Arial black.
The solution to this issue is:
1. Under Tools > Options > Environment > Views, find the Views section in the upper right corner.
2. Select either Mail* or Mail (simple).
3. In the bottom section, select Plain Text for both the Default Compose View and Font, and the Default Read View and Font.
You can select whichever font you want.
Disclaimer: As with everything else at Cool Solutions, this content is definitely not supported by Novell (so don't even think of calling Support if you try something and it blows up).
It was contributed by a community member and is published "as is." It seems to have worked for at least one person, and might work for you. But please be sure to test, test, test before you do anything drastic with it.