It doesn't have to be a red X (indicating an error state); many icon themes use a gray X. But really, it doesn't have to be an X at all (I'll change that in the description).
The true problem is that the only difference between the offline and online icons, which should be complete opposites, is a subtle transparency that shows up as a slightly different shade of gray. I spent the whole day yesterday "Offline" because the icon looks exactly the same as the online icon. Sure, it was more transparent, but how will someone notice the transparency when there's nothing to compare it with?
It doesn't have to be a red X (indicating an error state); many icon themes use a gray X. But really, it doesn't have to be an X at all (I'll change that in the description).
The true problem is that the only difference between the offline and online icons, which should be complete opposites, is a subtle transparency that shows up as a slightly different shade of gray. I spent the whole day yesterday "Offline" because the icon looks exactly the same as the online icon. Sure, it was more transparent, but how will someone notice the transparency when there's nothing to compare it with?