two options.
either remove the @erase_color attribute from the jit.gl.node box. this will clear the erase_color overide of jit.gl.node, meaning it's erase_color will match that of the jit.gl.render (the background color).
or set the alpha (transparency) value of the jit.gl.node @erase_color to 0, and set @blend_enable 1 and @depth_enable 0 on your jit.gl.mesh.
this will allow you to actually see through the mesh shape.