Grayflame

This weapon responds to channeled positive and negative energy. When the wielder spends a swift action to channel energy through the weapon, it ignites with a strange gray flame that sheds light as a torch, increases the weapon's enhancement bonus by +1, and deals +1d6 damage (as the divine power from flame strike) to creatures struck by the weapon. This flame lasts for 1 round for every d6 of damage or healing the channeling normally provides. When charged with positive energy, the flame is a silvery gray, good creatures are immune to the weapon's extra damage, and the weapon counts as a good and silver weapon for the purpose of bypassing damage reduction. When charged with negative energy, the flame is an ashen gray, evil creatures are immune to the weapon's extra damage, and the weapon counts as an evil and cold iron weapon for the purpose of bypassing damage reduction. This special ability can only be placed on melee weapons.