Product designer background object colour change with foreground overlay that also changes color

Hi there, I looked everywhere, but cant find an answer on this..please help me. I worked on your free version, and I love the way you developed it, just a  few questions please, my client sells flip-flops, and she wants to change the color of the flipflop that they can choose - ie. 7 different colors, while they are in the designer, as the first step, then do the design (with multiple images and text etc..) and then afterwards they can also change the color of the straps that goes between the toes..? is that possible? So its the flipflop bottom and the straps that must be color changeable?

Then the output file (for print) she just wants to take that and print without any die-lines whatsover or changing the size? - is that possible?

If you can please let me know it would be greatly appreciated?