Here's the thing.. the pictures of the fish you posted are not purples, they're coppers. It looks like the purple hue on them may just be because of the bad quality of the picture. MM's fish are not purples... they're multicolored. If you see a fish that looks "purple" but has any instances of red or blue on it.. it's just simply not a purple.
When it comes to animals you cannot classify based on phenotype (how it looks on the surface). You have to classify based on the genes... as it stands there is no gene combination that yields purples that breed true.
With that in mind I'm interested to see what your crosses yield. Copper does some strange things and the one picture of a "true" (or nearly true) purple seemed to have some copper in it.
In all honesty I'm skeptical about purples. There's been a lot of rumors about this and that breeder producing purples but as far as I've been able to find only one picture of a "purple" has surfaced... and that's in an article written in 2003 from a so-so breeder that never updated on her experiments.