For most printing processes, the color you put on your model in Blender has no impact on the color of the final print. For the FFF/FDM printers, the color of your print is going to be the color of the filament(s) you have loaded into the machine. SLA will be dictated by the resin being used. For the 3D Printing Service Bureaus, you may be picking a dye color when you order your prints.
The exception is the full-color printing 3D Printing Service Bureaus offer in Sandstone (gypsum powder) and now Plastic. Those printers need color information. In Blender, one way you can add color is by adding and assigning single-colored materials to your objects and faces.
