I used in game walls and saved them as a scene blank canvas. To move the walls into place I recommend using the movement tab for rotating and moving the walls. i learned the hard way to lock the floor and walls movement and rotation once i set it up before saving.
Then i just browse web for jpegs i like and apply them to wall / material/ texture /main texture select button. You will need to tile 1 for the horizontal and 2 for the vertical , as the wall extends below the floor. The tedious part is editing /cropping the picture into left center and right images for the three back drop walls. For the solid colors it's wall /material / params and choose diffuse color
Only done it once or twice, usually add an image into Blender, convert it to mesh (using face flip if needed) and then port the image over from Unity as a CUA.
