I wouldn't buy FSrepaint, you're far better off with the GIMP (freeware), though if you only want to do simple paints, FSRepaint might work for you. Myself, I use Photoshop, but that can be a bit expensive.
As for repainting the Skymaster, you'll have to use the textures from the all white scheme Carenado provided. You open those in gimp, apply your paints, ad then make a copy of the white texture, put it above your textures and multiply it. This will make the white transparant, but the panellines etc will remian visible above your paint, save as bmp, and convert them to something FSX recognizes using DXTbmp (another freeware program). You can make them either extended bmp's (so with alpha channel), or dds files, but for that, you need to flip the textures vertically before saving as dds.
Hope this helps,
btw, I made a few textures for the skymaster too:
you can find all of my repaints
here
JanKees