Nice screenshots!

Most people who makes skins use Adobe Photoshop. To make your own skin, first make sure you have the latest version of RealFlight installed, then in the menu click "Aircraft->Save Color Scheme As." You get to choose a name, and then you get a message telling you where the colorscheme .tga file was saved. Edit that .tga to get the look you want. Most G2 skins will work with G3 but some will not.

The aircraft designer program's release date has yet to be announced.