If you're looking for a bit of a change I think the purple low-lights in your black hair will look awesome.  Try this website for some inspiration, there's a model there with her hair entirely burgundy (or purple) which I think looks great!  (Note:  Don't skip the introduction, her picture is right in it). 

http://uk.lorealprofessionnel.com/_en/_gb/products/feature/site_majirel/Had - http://uk.lorealprofessionnel.com/_en/_gb/products/feature/s ite_majirel/Had

Had I the courage to dye my hair an "unconvencional" color I would definetely aspire to that model's hair.  Low lights that color will look great on black hair.  You could also try red if you change your mind.  If you are planning on doing this at home, just make sure you're careful not to stain hair where you don't want it colored.  Here's a tip I got from a hair magazine:

"The best procedure to obtain red high lights on black hair is to first bleach the hair where you want your high lights done.  By doing this there's no risk of staining the hair on unwanted spots.  After hair is bleached, do a pre-pigmantation (1 part red tinted color with 3 parts water).  This avoids the strands from absorbing or rejecting the pigment, which once again, prevents staining and makes the color last longer.  Only then can you use the final color."

That's pretty much what the article says.  Depending on the color you want (in your case purple) I don't think it's necessary to bleach it, as a matter of fact, I recommend you do a strand test first to see if the color sticks without having to bleach, try to avoid bleaching at all costs.  If a volume 20 peroxide doesn't give you a desired effect, try a volume 30 instead.  Also, try to get those foils for high lights, that way you can seperate the strands better.  Good luck and let us know how it turned out. ^^  

Okay, no problem, I'll just direct you through the website then.

Go to:

http://www.lorealprofessionnel.com/index.aspx - http://www.lorealprofessionnel.com/index.aspx

Then click on Great Britain on the Europe section, it should send you to the UK site:

http://uk.lorealprofessionnel.com/_en/_gb/index.aspx?UsrMd=0 - http://uk.lorealprofessionnel.com/_en/_gb/index.aspx?UsrMd=0

Then, on your far right, right under the search bar there's "products and advice", run your mouse over it and click on "products and services":

http://uk.lorealprofessionnel.com/_en/_gb/products/index.aspx?tc=Navigation^Nav_Products^Nav_products_services&UsrMd=0 - http://uk.lorealprofessionnel.com/_en/_gb/products/index.asp x?tc=Navigation^Nav_Products^Nav_products_services&UsrMd =0

Click on "colour" on the "in-salon services" area:

http://uk.lorealprofessionnel.com/_en/_gb/products/index_cat_S.aspx?Catcode=Axe_Salon^Axe_Coloration_S&tc=Navigation^Nav_Products^Nav_products_services&UsrMd=0 - http://uk.lorealprofessionnel.com/_en/_gb/products/index_cat _S.aspx?Catcode=Axe_Salon^Axe_Coloration_S&tc=Navigation ^Nav_Products^Nav_products_services&UsrMd=0

Now, go to the Majirel mini-site:

http://uk.lorealprofessionnel.com/_en/_gb/products/feature/site_majirel/ - http://uk.lorealprofessionnel.com/_en/_gb/products/feature/s ite_majirel/

It will open a seperate page where it has an introduction, do not skip that introduction because there's a picture of the model in it.  When the website goes to it's home page, click on "goodies" and it has the wallpapers of the models, that way you could have something to show your hairdresser if you like it.  Let me know if it worked.  I think if you decide to go ahead with it it'll look great!  Good luck. ^^