The technical difference is that digital color is always* a demosaic of a Bayer filter (or X-trans, or other filter), whereas color film has three layers of emu

The technical difference is that digital color is always* a demosaic of a Bayer filter (or X-trans, or other filter), whereas color film has three layers of emulsion to capture e.g. Red/Blue/Green. Lens focus is indeed very slightly different for each of the three layers. *There are a few other methods, such as prisms and stacked sensors, but in practice, Bayer/similar filters give better performance and that's what commercial cameras use.