I've been trying to get purple. I even resorted to a permanent, which didn't work!
I tried 'Colour Pulse' in 'Pepsy Purple' which is a temporary mousse, and it wasn't very good, so don't try that.
I've worked out purple is hard to get on black hair. As you have dark brown it might be easier though.
I've also worked out that 'big company' (L'oreal etc) dyes in unnatural colours suck. You're best off going for brands that make ranges of 'crazier' colours. (Directions, Crazy Colour, Special Effects, Manic Panic etc)
I've had best results with Directions' Plum. Nice purpley shine in sunlight. Special Effects' Deep Purple might be similar.
Oh, a word of warning if you haven't used this kind of dye before, they will turn your bathroom purple (or whatever colour you choose).
This was my hair in the sunlight after a few washes of Directions Plum