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Perhaps someone in your team uses steamy mist or some other stealth powers. Are you transparent all the time or just sometimes? You can ask for other players how they see your character.
Prunejuice is warriors drink.
When are they transparent?
If they're transparent only when in-game (as in, you're walking around with them), the game automatically turns them transparent if your view is immediately over-the-shoulder. Try zooming out a bit.
That said, if they're transparent at say, the character select screen, you're having some sort of driver issue and may want to contact customer support or post in Technical Issues.
Blue: ~Knockback Squad on Guardian~
Red: ~Undoing of Virtue on [3 guesses]~
This has happened on a second computer that I rarely play CoX on (if this is what I think you're experiencing). After Ultra Mode went live, I wanted to update the files on said computer and on the character selection screen, my alts were all invisible/transparent and you can barely make them out thanks to the dark green outlines.
Everything is fine though upon logging in and the problem went away after playing when you start the game up again. The second computer is running on a stock graphics card btw.
I just started my first City of Heroes account and for some reason my character is transparent and so are all of the other characters. They kinda look like ghosts. Anyone know why?