To make a place that makes you feel as if you just dove into the ocean, paint blue walls, add coral reefs and deep sea fish, and feature underwater . If you don’t want all that aqua in your space, you should have a white wall and then add some seashell decor to show off your underwater, deep blue sea and create a beautiful under-the-sea view. Showing off sea life is a great way to create, design an underwater interior and highlight the natural beauty of the ocean.