There doesn’t appear a way to apply a base color or texture to an Archimesh generated wall or room? Other than pre-canned textures provided in the Archimesh interface, can one further customize the wall cover?
EDIT. I fingered out how to do both color and texture in the Shader workscreen. Dooh!
Welcome 
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yes…as you discovered… just change or add some material and change to your liking…
( you may post a reply on your questions so you can mark this as solution… so other users will see that it was solved… this helps other users find this… or prevent them to look into this 
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Thank you for your support. Now here’s a head scratcher. Base colors or textures apply to both sides of an Archimesh generated wall. Is there a way to have a base color on one side and a different base color or texture on it’s other side?
Use a setup like this.
Plug your two materials in where the green and red are in the Mix Node. The bottom socket is (obviously) the back.
Outstanding! Thank you for sharing this technique.
Glad to help…
For some reason no one ever self solves more than one question. One of lifes mysteries… 
Dont forget to post the final render (in the Artwork section) so we can all ‘ooh and ah’.
I haven’t tried it out yet -working on it. The picture got me thinking. Wouldn’t the backface color be hidden inside the wall due to your example being a dimensionless plane rather than a wall of a thick dimension?
Hmmm. It doesn’t backface to the other side of a thick wall. Oh well. 
Obviously. For that you make a second material on the mesh and in edit mode assign the second side of the wall to it.
Me not thinking archmesh = thickness (because it was late at night) was where the confusion came from. Highly obvious now in the morning…
Make and keep a copy of the backfacing trick. You will want it for wine bottle labels one day.
Differing colors on the either side of a wall can be accomplished with Archimesh (but not Archipack). This side of the wall set to blue. The other side of the wall set to red.
Here, I’ve oversimplified the network of nodes, but you can roll your own obviously.
Enable the Archimesh add-on in Preferences.
In Archimesh create a wall.
Checkmark the Baseboard and Wall cover boxes.
Set the Baseboard Width to 0.0, Height to 0.050
and Wall cover Height to 0.050, and Thickness to 0.001
Essentially, you’re using the Wall cover option and setting its thickness very thin.
Bi-color walls works only on walls created as a Room by the Archimesh add-on because the Archipack add-on doesn’t provide the wall cover option when creating walls.
Shortcut keys to select the Room in Archimesh to create:
CNTRL A, M, A, R
UPDATE: Cycles resolves the slats of the wall cover in the Rendered viewport (which is an issue) while Eevee doesn’t. And unfortunately using nodes that are of the Environment texture type don’t get rendered by Eevee.
So it appears using Archimesh’s wallpaper option is not a satisfactory work around to applying a different color to both sides simultaneously after all. Oh well. 
