Cerokote is an interesting coating. If it gets oil applied to it unevenly, it can give a mottled appearance, much like you describe. It's purely aesthetics, and doesn't affect the functionality (or protection it gives) of the rifle. If it bugs you, just give the surface a good rub down with a rag/cloth. Like @scotch_egg mentions, it (the coating) is still prone to damage, but that just means it gets used and isn't a safe queen. I have probably about a dozen rifles that have cerakote, and the application process seems to dictate how durable the finish is. Some rifles show very little wear, while others show more wear (for about the same usage). <shrug> Any type of protective coating, whether it be cerakote, duracoat, DLC, etc. is very sensitive to how it was applied. I think what we are seeing these days, are that some companies are either trying to rush things, or have employees that aren't as meticulous as they should be in surface prep (which is absolutely critical when it comes to appearance and durability).
JMTCW...
