Is it permissible for a woman in her iddah (waiting period) to dye her hair with henna while she is in her iddah?

It is impermissible for a woman in mourning (haddah) to dye her head with henna, due to the Prophet's (peace and blessings of Allah be upon him) saying: "A woman whose husband has died should not wear clothes dyed with safflower or red earth, nor jewelry, nor dye herself with henna, nor apply kohl."