This would just give you a mixture of both parents.
Blue platy (BP) x Pineapple Swordtail (PST)
children: BP, PST, BST, PP
But i have a feeling that they would even be more mixed than that combo. They may even revert to the grandparents as well. Show some of the traditional Green swordtail coloration.
Genetics is still not a 100 % science.