Blue or yellow. You already have a yellow bowl on the counter, let that be your color guide. If blue you can go navy, cobalt or wedge wood. Then get dish towels to match, and floor mat with the color you choose. You have a beautiful kitchen. Some color will add pizazz.

As long as style remains sleek, you might choose any number of colours.

Or match to your existing things -

Have you looked at ikea?? Your kitchen is very lovely, it has a clean, modern feel. You could probably find a simple unit in their home office, bookcase area that would work for additional storage. I would measure the space carefully, you don't want it too wide, or else it will impede the walkway and feel crowded. I would say no deeper ( from the wall) than 18-20". You could maybe get 2 wall cabinets from IKEA, add feet to raise them up to 36" tall. top them with remnant of granite or butcherblock top and make your own storage unit that would not be more than 12 inches deep. Finish off with matching handles to your existing cabinets.