Like with a lot D&D lore, I've never been too enthusiastic about the dragons they give us, so I never knew that if they went against their inherent alignment it is physically manifested. Very interesting. If that's true of Devils and Fiends too, why doesn't that manifest in Tieflings? I'm always confused when the metaphysical translate into the physical in situations like this. Or doesn't not happen with Devils? That's interesting too.
It used to be that tieflings couldn't be of Good alignment due to their heritage, but that was changed in later editions. Makes no sense to me, they are planetouched after all, they should be influenced by the evil planes, but I suppose too many people wanted to play a good unjustly persecuted underdog. It's a shame because tieflings don't have a culture of their own, so without the influence of their bloodline they don't have much to set them apart lore-wise. You have this cool evil heritage, but the only thing it does is give you horns, a tail, and a couple spells. Boring!