iraq was called sawad because of the greenness of the palm trees there. and his saying every last night he means the last nights i.e. forever just as you say i will not speak to soandso the last nights i.e. as long as there is one night left of time. and he also said mentioning lightning
وقيل للعراق سواد، لخضرة النخل بها. وقوله كل آخر ليلة ، يريد آخر الليالى أى أبدا؛ كما تقول لا اكلم فلانا آخر الليالى، أى ما بقيت من الزمان ليلة. وقال أيضا يذكر برقا