I also breed platies, though not so specifically as you're trying for. I did end up breeding a blue MM platy with a red tiger platy that had a twinbar tail though. Got a mostly blue platy with a red dorsal fin and a cross between mickey mouse and twinbars with darker stripes and spots on his body on one side. lol I've also gotten some sorta purpl-y blue ones breeding blues with reds.
I'm am debating on trying bumblebee platies with red platies or blue just to see if I get anything odd. lol I'm more for odd colors than patterns, but I have gotten odd patterns before.
I also do mollies and ended up with some black gold dusts breeding gold dusts with dalmations, and some gold ones with scattered black shadowing and spots. It's quite fun, but you don't want inbreeding and want nice healthy parents, even if the babies don't exactly come out pretty, they'll at least be healthy. ^^; My best was ending up with what I call calico mollies, they came out orange black and white, and rather pretty, with lyretails, and also some silver lyretails mixed with creamsicles that came out pale yellow or silver with red or orange spots and markings. And some that come out black and white, kinda like pandas...
Just a tip for you! Try to get your fish from different shops, less inbreeding chances, especially get males from different shops than females at least. Buying males and females from the same shop often results in the occasional deformity.
I would love to see photos when you get started and of your fry!
Here's a few examples of my oddities. I really want to see how yours come out. Sorry, the one of my "Blue Tiger" isn't too great, he never holds still.
My creamsicle/silver lyretails, one male and one female, female first:
My panda, he came out worse than the blue tiger. ^^;
Please share your results! :3