I have been learning "inkscape", an extremely powerful free graphics program (they will accept donations which I will do, it is wonderful) many of these programs are difficult to master but this has very good tutorials and will take quite a while to master, but shading, twisting, textures etc are all possible from cartoons to portraits to text. I have been designing my logo and color scheme for SkyView Lines. I want to get white decals printed and this program creates the type of files that the printers want (svg) My general color scheme for locos and proprietary rolling stock will be the green hills against a blue sky with a stripe of darker blue for the frame and lower details. The logo will be white. For passenger cars and locos I will also make some white decals that have this lettering:
easy to download when you open the first page find help then find tutorials they are very important and well written this program is sophisticated enough to require really learning it but then the sky is the limit for effects good luck