There is no need to mitigate it. Mold - actually fungal growth - on mulch is completely normal and to be expected. Just a visible sign that fungal organisms are digesting the organic matter of the mulch and is harmless to plants. It is just more obvious in wet/damp weather.

If you feel the need, you can just disturb the mulch by raking lightly and it will vanish. But if conditions are right, it will be back again.

Instead of throwing the espresso grounds in the compost bin, I guess I'll start saving them to topdress the mold.....so at least it's brown and not the color of what it is now...