Mistro,
There are a great many tutorials around for repainters, here is another one -
http://mainescenery.proboards.com/index.cgi?board=paintIn terms of coloring pixels most of what you find for FS9 applies to FSX also.
The primary difference in the 2 sims is texture format.
Both use formats of .bmp files that Photoshop cannot read. This is where DXTBmp comes into play. It will convert files to a format PS can edit, then convert them back to something FS can use.
There are also tons of tutorials on the Internet for PS also, that may not apply directly to FS, but will expand your abilities.
Dive into repainting FSX defaults, the files you want end in _T. Don't worry about reflections, bumps, and specs untill your comfortable with the basic textures.
Another tip is to download others repaints and compare them with the defaults to see what they did.
Good luck and happy painting,
Joe
PS. Be careful, this can become quite addicting.