What is the ruling on using nail polish during the mourning period (iddah)?

A woman observing the mourning period (iddah) for her deceased husband must abstain from adornment, including nail polish (manicure). This is based on the prohibitions found in the Prophet's Sunnah against wearing dyed clothes for adornment, using kohl, perfume, and henna. Scholars have unanimously agreed that a mourning woman is prohibited from anything considered an adornment, whether it be in clothing or on the body. Nail polish is an adornment, and therefore she is prohibited from using it.