To dye hair, advise for men and women

It is mustahab (commendable) for men to dye their head and beard.
There are fourteen advantages for women in dyeing their hair and applying
henna to their head and feet:
a) Deafness is cured
b) Brightness in the eyes is increased
c) Dryness of nose is lessened
d) There is good breath in the mouth
e) Gums are strengthened
f) There is no bad smell in the under arms
g) There is less temptation from the devil
h) The angels are happy
i) It is a means to the happiness of a momin
j) The nonbelievers get jealous
k) It is beauty in itself
l) It is good scent in itself
m) It is a means to the salvation from the curse of the grave
n) It makes Munker and Nakeer feel shy
According to a tradition, a certain person visited the Holy Prophet
(s.a.w.a.) and when the Holy Prophet saw a few white hair in his beard,
he said that these hair are light and all the muslims who possess a single
white hair in the beard, there will be a light for them on the day of
judgement.
According to another tradition, Hazrat Ali (a.s.) said that he did not
apply dye (khizab) as he was mourning for the Holy Prophet (s.a.w.a.)
Another reliable tradition states that Imam Ja'far-e-Sadiq (a.s.) said
that among a few bad signs o which will appear in the world during the
last days will be that men of Bani Abbas will act like their women by applying
henna to the hands and feet and comb like them.
According to Imam Ja'far-e-Sadiq (a.s.), the Holy Prophet (s.a.w.a.)
ordered every woman to apply henna whether she was a widow or a
happily married woman, the former as not to let her hands resemble
men, the latter to beautify them for her husband.

-Allama Majlisi's Tehzee ul Islam, Part 2, Ch.11