Well, I also found this out:
You Don't know if they're Shiny until they're purified.
but A glitch in Colloseum (Not to be off topic)
Some pokemon Aren't shiny until they're purified, but I actually found Shadow Tyranitar in the Alternate color, BEFORE IT WAS PURIFIED!!!!
But the Odds are still high, but I found 5 shiny Pokemon in XD, so I'm guessing 1 out of 1355.