i find the boxed hair colours tend to make my scalp burn. i found that the stuff my hair stylist used (i splurged for the first time and got it done professionally) did not...it seemed to be not as harsh and smelled a lot nicer (didn't burn my nose and eyes) so you may want to check into that if you can afford it. also, if you are dying your hair black for the first time, easier to do on short hair (that way, if you decide you don't like it, it doesn't take as long to grow out...lol) and i have yet to find a 'temporary' black haircolour.
i like dying my hair too, i have it black now (naturally light brown) and now have fun putting blobs (for lack of a better word) of colour in...my next colour is going to be fuschia....and then maybe a nice shade of blue. manic panic colours are great for that...they only last a couple of weeks, then you get to change them... 
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friends are like balloons...once you let them go, you can't get them back.
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To the world you might be one person, but to one person you might be the world.