Yes, additives are present in color films (and sometimes in color developers) to prevent image spread. If they are not present, the dye clouds can be too big. In fact, in the absence of these chemicals, you can have dye contamination between layers. You can get a magenta dye cloud become so big that you get cyan and yellow dye clouds in adjacent parts of the coating. So, color is a more complex best. A common developer additive is Citrazinic Acid (E6) and Sulfite (All CDs).

Now, back to your observations about B&W. The example I chose was done on purpose. You see, grain can interfere with sharpness. So, you can prove on paper that a film is sharp, but when you see the grain it is similar to aliasing in digital.. Yep, quite similar in some aspects, but not overall. So, this is why Kriss came up with Image Content. Or, how good does a given image look when you combine gran with edge effects and vary their contributions to the quality of what you see. This can be reduced to a mathematical formula which is now in use at EK. This treatment will single out the optimum combination of multiple effects such as halation and light scatter and add them to the mix of grain and edge effects.

But, there is more to this than the above. You see, modern B&W films are made up of 2 or 3 components and modern color films have up to 9 imaging emulsions. Each of those will respond differently, and thus we must look at the edge effects of the slow, medium and fast components for example. And that is folded into the grain of each. And these are folded into the overall result of the full multilayer. This is a lifetime of learning when you build a film.