I met a sister in Turkey, dressed in black. When I asked why black, she cited a Hadith. What is this Hadith? Do women need to dress in black? I read a Hadith that our Prophet preferred white. Can women dress in white? Can you explain the importance of color in dress? If color is related to being less attractive, it may be that in some countries black may be more attractive than white. What do you think?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

The most required quality in the dress of the Muslim woman is that it should be large and thick enough to cover her complete body. It should also be modest and should not be similar to men's dress. The colour or the quality of the dress does not have any importance as long as this dress meets all the above conditions.
As for the Hadith the sister mentioned in which the Prophet asked Muslim women to wear black coloured clothes, we do not know any Hadith with this meaning and we do not know any Scholar who urged Muslim women to wear black clothes. But there is a Hadith proving that wearing black coloured clothes is permissible. Imam Bukhari narrated from Umm Khalid she said: "Some clothes were presented to Allah's Apostle as a gift and there was a black Khamisa with it. The Prophet asked (his companions), "To whom do you suggest we give this Khamisa?" The people kept quiet. Then he said, "Bring me Um Khalid." So I was brought to him and he dressed me with it with his own hands and said twice, "May you live so long that you will wear out many garments."
A woman is not obliged to wear a black cloth since the evidences prove that any colour could be worn if it meets the above Islamic conditions.
As for the Hadith you read and which urges Muslims to wear white clothes it is a sound Hadeeth. The Prophet said: "Wear white garments, for they are the best and the cleanest and you enshroud dead in them".
As for your question about women wearing white clothes we did not find any evidence prohibiting wearing white colour for women, as we did not also find any scholar who prohibits it. But one should be careful of two things:
1. If the woman is in a country where women do not wear white garments and only men wear them, it is better for women to avoid wearing clothes of such colour to avoid imitating men, and to avoid a dress of fame or celebrity. The Prophet prohibited it. The Prophet said: "If any one wears a garment to gain fame Allah will clothe him in a disgraced garment on the day of Resurrection". The scholars said: "Every garment which is unique and not similar to the general garments of people is considered as a garment worn for gaining fame".
2. A woman is asked to be well covered and dressed modestly. No doubt, that colours other than white are more appropriate for this purpose. As for preferring the white colour it is desirable as mentioned above. Muslim scholars like the green colour too for the Hadith of Abu Rimthah he said: "I saw two green garments over the Prophet". Moreover this is the garment of the dwellers of The Paradise. Allah Says (interpretation of meaning): {Their garments will be of fine green silk, and gold embroidery.} [76: 21].
Some scholars dislike wearing pure red coloured clothes and clothes dyed with saffron while others do not dislike them. There are Hadiths that the Prophet wore a red garment, and other Hadith that he wore two garments dyed with saffron.

Allah knows best.