You can define conditions for face customizations, like "terminal mode" or "minimal colors" in the customization editor:

When customizing a face, click the [State] button and select "Show all display specs". Then you can set up the conditions for further specialization of the face.

For me, this resulted in this snippet to set the background color
to **black** when the frame is a tty.

    (custom-set-faces
     '(default (
                (((type tty) (min-colors 256))
                 (:background "black"))
                (t
                 (:background "#181a26")))
        ))