Piercing Cold Vs. Protection Spells

[shaka gl]

So, my party just engaged with a elemental Savant (Cold) with the Piercing Cold feat. They had Protection from Energy (Cold) cast on them. But, as a DM, if this feat normally hurts people INMUNE to cold, i think it should hurt people PROTECTED form cold. Although its also possible that it only works for things naturally protected or inmune, not magically.
I dont really know what to do.
What do you think?

[Curmudgeon]

It's right in the feat description (Frostburn, page 49). Resist Energy (cold) has no effect against a [Cold] spell with this feat. There's no mention about Protection from Energy (cold), so it behaves normally ("still entitled to whatever other defenses the attack allows"). With the increased damage the feat affords, the protection isn't going to matter much.

[tyckspoon]

I think you get half damage, as normal for 'creatures normally immune to cold.' The only source of immunity the feat bothers to call out as working any differently is the Cold subtype, which still isn't affected.