With many pieces of Mdina the colour perceived will depend on whether the item is backlit or not - whether light passes through the item or it bounces off the surface, the effect is dichroic. To show that effect with the paperweight required a strong source of light - in this case the paperweight is sitting on my phone.
In these two photos of the same vase the first is backlit - the light source is behind the vase, in the second the lights are in front next to the camera.