The grey blotches are not due to the particle load in the ball. They are called phasing, and I personally am not exactly sure where it comes from. It is either the finishing process, or the coverstock curing process. The reason that I can be definitive in saying that it has nothing to do with particle load, is the fact that I have seen reactive stuff with similar phasing.
Whatever the case, I haven't seen any difference in balls with pronounced phasing as compared with stuff without, or with minimal phasing. To remove such marks, you can use acetone (technically illegal), or you can hit it with some powerful ball cleaner, such as LaneMasters cleaner.
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