For sandwiches, you can add a drop of red or green food colouring to the paste. Again, mix well before spreading on to the slices of bread.
You can add mayonnaise to make it creamier as in the filling for puffs
You can add grated carrot to the cheese paste: Add some grated carrots to this mixture and blend well until smooth. The more carrots you add, the deeper the colour. The carrot is a good natural substitute for the food colouring.