I don't have an answer, but I do have a tip.

Think through your projects before you start. Anticipate problems and find solutions before you start.

Your post and beam project, and this one, show you are jumping off the diving board, then checking if there is water in the pool on the way down.

The look of your work suffers as a result.

I would go over. See if you can find a light gray outlet and plate so it blends a little more.

There will be some gaps around the plate due to the nature of the brick.

The brick under the right receptacle is notched. The matching brick under the left receptacle isn't Replace the right brick. If you fill with mortar flush with the brick surface, you can easily use covers over the brick. If you don't want that overall look, pipe grout up to the brick face at the outlets.

Just a heads up that brick makes a terrible backsplash because it will fill with gunk and bacteria and cannot be properly cleaned.

If you are not going to purge the brick . . .

Too late for your project, but it might help others ... plugmold under the upper cabinets would have been the solution to your problem.

Definitely, on the outside, this is when boxes with adjustable brackets come into play they can be adjusted from 0" to 1-3/4" and if they don't use them, they have to use extension boxes.

As I mentioned on your other post brick is not a good choice for backsplash and if you insist then there are gaps not matter what choice you make and Lutron makes many colored receptacles and plates so find one as close in acolor as possible for the brick. Sorry but really tht brick and counter do not work together IMO

Since your brick is not an exterior application you might consider applying a penetrating sealer. That should help with cleaning and prevent (to a degree) liquids absorbing into the brick. As for the outlet covers my vote is a cover that will sit on top of the brick.

You needoutlet box extenders first of all. Second, you need a Lutron orLeviiton outlet that is NOT White, with color matched face plate. Then to cut away anything that interferes with the plates attaching. Third, you can try using a penetrating sealer to help with the major issue of the texture trapping staining dirt, but that only slightly helps. It's the texture that's the culprit.

Yes on the outlet extender. Then I'd hire a decorative painter who can match the finish of the brick on the outlet covers. I've done this in a previous client's kitchen when there was a mosaic tile backsplash. Worked like a charm and the outlets were camoflauged.