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.