MTG Salvation

Ok so i recently started playing MTG, i was playing a casual game with a friend. I was using a white/blue deck. I stumbled upon this artifact called millstone. This is when i was introduced to milling. Nothing makes me more happy than milling someone, seeing their smile fade when the top card of his library is a planes walker and he has to discard it. Since that day i have been determined to make a mill deck but to do that i need to know the colours which would best suit this play style. I heard that blue is best for milling but black has some good cards as well. So i was wondering, mono blue or blue black. I don't really care what set it is from either. Thanks in advance !!