I don't ask this to be narky, but how much prototype track have you seen? I've seen track on the Dao line in Portugal that had neat and well-defined alternating bands of light and dark ballast, each about 30 feet in length. I couldn't find anyone who could explain that!
Bear in mind that I'm trying as much as possible to only model things that I've actually seen for myself, I'm not just making it up as I go along... :-)
That's probably the case. The effect on the actual modules is not that pronounced.
As far as I'm aware, there is no ballast on top of the sleepers on my modules. I went to some trouble to keep the ballast below the tops.
But having said that, it's not at all unusual to see replacement sleepers with old or weathered ballast around them. Ever seen a per-way gang re-sleepering, as opposed to relaying? I've watched blokes remove the spikes, dig the ballast away from the end of the sleeper with a pelican pick, remove the old sleeper, put in a new one, all the while barely disturbing the surrounding ballast. They do it in Japan, and we do it here in Australia, so I'd hazard a guess and say it's done that way elsewhere, too.
All the best,
Mark.