To design a home that looks as if you just went diving, paint blue walls, add corals and deep sea fish, and display oceanic . If you don’t want so much blue in your room, you could have plain walls and then add seashell decor to accent your oceanic, deep blue sea and make a perfect under-the-sea room. Exhibiting sea life is a great way to make, design an underwater interior design and showcase the beauty of the ocean.