I don't think so, it has to be done quite deliberately. It feels like they're doing it purely to mess with my head. I don't see that they gain anything by doing this. I wish FD would just take the white option off the font menu.
Perhaps...but it is a common mistake I've seen.
Even Zac did it once.
Basically, it goes like this
Precondition: Using Default forum them with black background and white text
1. Type up post in advanced editor, click preview
2. Click Submit
3. Forum throws up on itself and fails to post
4. Panicked, you copy your post from the preview mode
5. Browser dutifully copies but it also copies font values, such as color and font type
6. Restart failed post
7. Paste in what you saved
8. Browser pastes in font information that it copied...(you copied white text, I give you white text)
9. Submit post
10. Still using theme with black background, all is good
11. Monk, who uses the pastel them, rages while trying to read white text
EDIT: Basically, if you use the standard unformatted text color, the forum automatically applies the right color for the theme used. If you define text color, as would happen in a copy/paste situation, that color is maintained no matter the theme being used to view it.