change theme of imported slides from another keynote

I have several keynotes, all with different themes. I want to import a couple of slide from one and import to another, but am unable to change the theme to match the keynote I've just imported.

When I right click and select reapply the master to the slide, all I get is a font change and not the full theme being applied.

On the right hand side where the all new inspector is it tells me the theme has been chosen and all is well, when it is not. I used to be able to change this in the previous version of keynote, but just cannot a) remember what I used to do b) work it out on this new version.

I have attached a screen shot if it helps.