All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, the question is not clear and we are not aware of anything that is called ‘white fasting’ in the books of the jurists. However, if what you mean is fasting the Three White Days (i.e. the 13th, 14th and 15th of each lunar month), then this is a recommended Sunnah.
Nonetheless, the Sunnah when fasting in general is that the fasting person breaks the fast with ripe dates if any, otherwise with dry dates if any, otherwise with water, as Anas said: “The Prophet used to break the fast with ripe dates before he prays (Maghrib prayer), and if there are no ripe dates, he used to break the fast with dry dates, and if there are none, then he breaks the fast by having some sips of water.” [Ahmad, Abu Daawood and Al-Tirmithi]
If you break the fast by eating other things than what is mentioned, your fasting is still valid and you are not sinful but you miss the reward of following the Sunnah unless you habitually break the fast according to the Sunnah but you did otherwise due to a sound reason, like sickness and the like, then you will be rewarded in any case as the Prophet said: “When a person falls ill or travels, the same reward will be written for him as the one he gets for performing good deeds when he was a resident and in good health.” [Al-Bukhari]
Finally, it should be noted that eating only fruits as a way of seeking treatment and the like is permissible, but if you believe what some people believe that meat is unlawful, then please refer to Fatwa 88860.
Also, for more benefit on the excellence of Sahoor (i.e. the pre-down meal), please refer to Fatwa 86920.
Allaah Knows best.