Dreaming for Istikhara, is a practise without a base in Islam!
Istikhara الاستخارة means to want khair (good). Istikhara is to pray to request Allah’s help in an irresulate subject and situation. For this, Rasoulullah recommended to pray a salat for 2 rakahs and pray a special prayer after it to request khair from Allah (al-Baqarah 2:153; Bukhari, Tahajjud 25, Daawat 49, Tawhid 10; İbn Majah, Iqamah 188). However, to sleep and get a sign from the dreams is bid’ah (something that has been introduced into the religion of Allah that has no general or specific basis to support it)! Seeing red or green signs in dreams is based on individual experiences, not on the Islamic source. (Prof.Dr. Salim Ogut, “Istikhara,” Encyclopedia of Islam, Diyanet (Turkey), XXIII, 334).