Match/blend them to the backsplash tile so they disappear as much as possible. They are utilitarian and not design elements that need to be highlighted.

match the outlet direction to the tile. If you have horizontal tile, like subway, place the outlets horizontally. If the tile runs vertically, place the outlets vertically.

I have white covers & outlets over white subway style - any contrast or different color between them & tile will make them ’pop’. You can find almost matching color covers on line. I also had my outlets placed as close to counter as possible so they aren’t at ’eye level’ when looking at backsplash. I also had the outlets & covers placed horizontally instead of the usual vertical placement. This makes the outlet shape mimic the subway style tile.

"match the outlet direction to the tile."

^^This. I regret not doing that, my electrician talked me out of it but I should have stood my ground on that one.

My outlets don't match the tile (I have green tile with slate outlets). With your color tile, I'd go with a white that isn't too blinding of a contrast or a light grey; as mentioned, you can get outlets in all kinds of color.

Thanks everyone, I did white outlets so I think I'll change to white covers. The grey in til is very light.