While it is true you can get purple with fuming it on, you have to do it in stages. What I mean to say is fuming only happens with certain metals. most of them have to be pure and usally a presious metal like gold, silver, copper, platinum, etc. Certain elements will also fume but can be more toxic than others so you have to be very careful what you are choosing to fume with.
Each color is achieved by the saturation or how much you fume it and its reaction in the flame. for example with gold I have been able to get anything from a light pink to a deep red. With silver you can get anything from a bright yellow to a cream white to traces of blue. Fuming is never an exact thing.
I got purple from first using pladium which leaves a gray smoke color on clear glass. Then by smoking gold over that you get purple. Its reproduceable and constant so I know it works.
Here is another tip for you: gold being quite expensive these days, I found that if you buy the 2gram gold in a bottle (fire on gold for ceramics)
20.00 per bottle. then make up a bunch of Lolli pops. (glass mass smashed flat on the end of a glass rod) paint them up with gold from the bottle. this gives you gold lolli pops. Then heat the item you want fumed first. then put the lolli pop in the flame (low neutral flame) the trailing edge of the flame is forced to redirect from the lolli pop to the item you are fuming. this will transfer the fume quicker and more direct to the item. Works good and a little gold in a bottle will go a very long way. I can use the same lolli pop for about 4 or 5 applications.
Good Luck
Toast