Praise be to Allah.
It is permissible for a woman to dye her hair any colour other than black, so long as that is not imitating non-Muslim women, such as if non-Muslim women or some non-Muslim women have a special way of dyeing or cutting their hair, and that is exclusive to them; it is not permissible to imitate them in that case.
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) was asked: Is it permissible to dye parts of the hair such as the ends or the top only?
“If the hair is to be dyed black , the Prophet (peace and blessings of Allah be upon him) forbade that when he told someone to change his white hair but to avoid black. He said: “Change this white hair but avoid black .” Sahih Muslim (5476). A stern warning was also narrated for the one who does that, which is when the Prophet (peace and blessings of Allah be upon him) said: “There will be people at the end of time who will dye their hair black like the crops of pigeons; they will not even smell the fragrance of Paradise.” Narrated by Abu Dawud (4212) and al-Nasai (8/138); classed as sahih by al-Albani in Sahih al-Jami’ (8153). This indicates that it is haram to change the hair colour to black. As for changing it to other colours, the basic principle is that it is permissible unless it is done in the manner of non-Muslim women or immoral women, in which case it is haram for that reason, because the Prophet (peace and blessings of Allah be upon him) said: “Whoever imitates a people is one of them.” (Narrated by Abu Dawud (4031) and classed as sahih by al-Albani in Irwa al-Ghalil (5/109).” (Majmu’ Fatawa wa Rasail Ibn ‘Uthaymin, 11/120)
And Allah knows best.