Answer:  My thoughts having witnessed the problem: – The black mulch looks great the first month/year, but then it makes it very difficult to keep looking good because it is hard to remove all debris to make it look nice.
Like maple helicopters, small leaves, pine cones, spruce needles, pine needles, small twigs, and other tree stuff – all these things turn brown. So when you see them on top of the black mulch it looks untidy.
Unless you take all brown debris off, which is impossible. We try, usually just wind up taking a lot of black mulch away with each cleaning. Go outside tomorrow and look at all the stuff that is on your flower beds, and for the most part your flower beds may look tidy enough.
All this stuff that you see will be on top of your expensive new black mulch.

Natural cedar mulch combines with this debris and it all blends.

I am converting a customer’s existing black mulch garden this year to a cedar mulch for this reason.

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