Yes that is correct. If your game produces a shiny egg, it will always hatch shiny. So, if as you said, egg 50 is shiny, you can turn off you game, pick up egg 50, and hatch it where every you want. I RNGed about 30 eggs for someone a year or so ago, and they hatch shiny on my game, but he wants them in eggs so they are still in the eggs. Regardless, if i were to hatch one, or even all 30, they would still be shiny, and yes, i hatched them all already just to verify they were right, then turned the game off without saving. I have also hatched themn all again since (because i forgot which one was which and what the exact details were) and they were indeed still shiny. Don't worry, you will not lose a shiny as long as you save before it hatches. Well, if you trade that egg away it probably won't be shiny on the next game, but that isn't at issue here.
Unless your talking about gen 4, like Dangertrout pointed out earlier, that is incorrect. The game does not check the PID against the ID/SID combo until the egg hatched. Even in gen 4, if you trade the egg to a different game, the egg will not hatch shiny on the other game. The reason you can be certain that once an egg hatched shiny on your game it will always hatch shiny is because the PID is set once the egg is collected. As long as the PID, ID, and SID don't change, the egg will always be shiny.
Oh. well that's not that different. I thought it was always shiny when you got it though :/ oh well. Just don't trade them
@4th Kira good luck. your avatar is disturbing. XD