RGB is the color model that all electronic devices use to reproduce color, such as televisions, computers, phones, tablets, etc. RGB files are suited for electronic presentations created in PowerPoint, Word, Key Note, Prezi, etc. or any Internet-related needs.
HEX colors are used for specifying colors within web pages. In most cases, you can use the RGB files for this purpose.
Portable Network Graphics is a file format for image compression that is widely used on today’s Internet. On this page they have a transparent background.