Wonderful topic! Suezz is right NEVER go darker it ages you. I have short hair and do it in the bathtub while I am reading a book.lol
Sometimes I add candles to the room to give the luxury feel while I am changing the color from grey to something more youthful. I just read that you are to wet the hair with tap water before you go in the pool to keep it from turning green as hair absorbes the first thing on itYou also want to vaselline you skin where you don't want the color in case it runs. I am not an expert but this was learned thru trial and error.