i think a dark chocolate would look awesome.
one bit of advice though (i went from blonde to brown at home once and it went terribly wrong). if you can afford to do it at a salon, do it!!!!
otherwise, call the number on the box first, tell them you are blonde and going dark, they will probably get you to buy another box of red and use the pure dye as a filler (so the colour has something to grab on to). if you dont do this, chances are your hair will either turn green, or the colour will fade to a greyish weird shade within days. last thing, make sure you buy enough boxes to saturate your hair, i used to work as a cosmetics beauty adviser and sooo many girls would come in with long hair and only buy one box, then come in 2 hours later asking me what they could do since their hair wasnt covered evenly
good luck!!!