Adding appearances in Assembly mode.

I'm adding appearances by dragging them from the appearance library on the right and then dropping them on the face/feature/part that I require.

However when the little flyout appears and I select 'part' the whole part turns black and it doesn't show the apperance.

Have I inadvertently clicked something, I'm hoping someone can shed some light on this for me. (Excuse the terrible pun!!)

SolidworksGeneral