But by the time she joined the Justice League, she looked like this...for some reason.
After she dropped out of the spotlight her appearance changed a couple times, and by October 2004 she had this very generic look:
But right after that (December 2004), she appeared in the Justice League Unlimited episode "Wake the Dead", where she more closely resembled her classic appearance, but with a more modern haircut.
Vixen went on to have several guest spots on the show, with the last one being the episode "Grudge Match" (March 2006). Just a few months later, she joined the Justice League again in Justice League of America #0 (August 2006) with a very similar look:
She later appeared in the New 52 with a similar but not quite the same design, although with her having a completely different costume in her upcoming animated series, I'm curious to see whether her comics self will once again follow suit (no pun intended).