Adding a shape to a 3D plot

Is it possible to add a shape to a 3D plot?
I am trying to add a “floor” to my 3D plot. I tried using add_trace with a shape, but not having any luck getting the shape to show up. Should this work? or is there a better approach. Basically, I want to add a little color to the z plane, so its clear which way is up and down in my plot. thanks

Shapes can be inserted only in 2D plots.
But you can plot a colored z-plane, defining it as a surface:

import  numpy as np 
import plotly.plotly as py
x=np.linspace(0,2, 50)
y=np.linspace(1,3, 50)
z_level=1.0#plot a z-plane at height 1
single_color=[[0.0, 'rgb(200,200,200)'], [1.0, 'rgb(200,200,200)']] 
z_plane=dict(type='surface', x=x, y=y, z=z,
                     colorscale=single_color, showscale=False)

is this still impossible, or has this functionality been implemented in the past years?