If we understood correctly, Blender does not allow more than one domain for fluid simulation in a given scene. This means that any inflow (fluid) object will be transformed into only one domain object as the final simulated fluid. That is, regardless to any material assigned to inflow (fluid) objects, ultimately the domain material will apply. This causes difficulties to experience mixing fluids as questioned here.
In our recent trial in the following figures in order to simulate two different types of fluid (i.e., different material, etc) we simulated each separately and baked. Now we question how we can use the resulting images to put the fluids together in one animation? We tried to composite but didn't get acceptable results. Is this the correct approach or is it possible to bake multiple simulations in a scene?
Note that before we end up with separate baking we played sometime with multiple scenes, different layers but no success in putting two fluids together!