My eyes are also dark brown. I love to try several different colors of contact lenses. Purple is a great color to try, which makes your eyes very beautiful. Yet if you would like to wear the color contact lenses for working time, I suggest you can also choose a pair of dark brown ones, just for working time. It looks very natural, and makes your eyes shine too. Purple ones, you can wear them for casual time. Yet I recommend you consider some online stores. They are much cheaper, and if you are not satisfied with the color you chose, you can make refund easily. Sometimes you can get product for free. The linkages below are for your reference.
http://www.coastalcontacts.com/
http://www.framesdirect.com/