How to get this color dye (purple) for the tips of my hair?

Sounds pretty cool what you wanna do...I have two purple streaks in my hair that are EXACTLY that colour...I forgot the name of the hair-dye i use, but I know that you souldn't use Wella...it's more of a purple-violet colour (if you know what I mean....It washes out to a more reddish pink colour, and it washes out in a matter of a month, I used it before)...the purple I used (because I decided to switch namebrands) isnt mixed with another blue, it just came out that colour, and it lasts over 3 months....so good luck and have fun!