We recommend saving your print files as PNG. PNG allows you to preserve transparency,  maintains resolution, and is a modern, universal format. 
To save your print ready images in Photoshop or Paint, go to File > Save As > PNG. In Illustrator or Draw,
you must export your image, go to File > Export > PNG.
If you are creating your own artwork in a raster program always ensure you have a transparent background layer.

When exporting from a vector program, size the artwork to the approximate print dimensions,
and export as .PNG at 300dpi.

RGB color method.

Whit sublimation printing the white color is never printed.