I once had success with three different colour pastes which I piped onto Ritz biscuits. They looked nice and were very quick to do, and to top up if necessary. You can make the pastes and fill the piping bags in advance, but be careful to keep them the right consistency. Some will go too hard in the fridge.
You can make them by blitzing up liver pâté, various mixtures with cream cheese, blue cheese, tuna, olives, peanut butter, tomato paste or sun-dried tomatoes etc etc. Add butter to soften if necessary. I don't bother with further decoration, although you could put a little bit of e.g. olive, radish, parsley on top. They look nice enough without in their colourful pinks, greens, blacks, whites and yellows.