What I do is...........
1) Place the ship in the Model Viewer and move it to the desired position.
2) Use the PRINT SCREEN option
3) Open MS paint and paste the mod viewer image
3) Crop it to the desired size IE just the ship with blue backround.
4) Select the backround color I want and FILL in the blue area
5) Save the new image
Instant quick beauty shot. As for the renders with planets and such ..... those folks use a more advanced texture program like PSP or Adobe etc.
-MP