I like the tile you currently have, though maybe not the grout width on the floor. The new vanity will look great, especially if you can float it. I would prioritize fixtures over tile if you are on a budget. If you're set on changing out the tile, I think of mcm bathrooms as having rectilinear tile or more organically shaped natural materials like slate. Color is fair game - there were lots of bold colors used in that time period, or you might argue that using natural materials is keeping in the spirit. I don't know about herringbone and diagonal tile. Herringbone strikes me as more Remodelista than Dwell. Which is nice if that's the look you're going for. Diagonal tile can look gimmicky if it doesn't relate to the rest of the house. Here are some color ideas: [Modern Bathroom[(https://www.houzz.com/photos/modern-bathroom-ideas-phbr1-bp~t_712~s_2105) by San Francisco General Contractors Moroso Construction [Modern Bathroom[(https://www.houzz.com/photos/modern-bathroom-ideas-phbr1-bp~t_712~s_2105) by San Francisco Architects & Building Designers Swatt : Miers Architects [Midcentury Bathroom[(https://www.houzz.com/photos/midcentury-modern-bathroom-ideas-phbr1-bp~t_712~s_2115) by Mountlake Terrace General Contractors W. S. Feldt General Contractor, Inc. [Contemporary Bathroom[(https://www.houzz.com/photos/contemporary-bathroom-ideas-phbr1-bp~t_712~s_2103) by Melbourne Kitchen & Bath Fixtures apaiser

Sorry took so long to update....These are some photos of the bathroom, although it was still not completely finished at the time these were taken. The door and shelves have been stained a Carbon gray gel stain that almost perfectly matches the vanity. I used 8" white shiplap through out. The wall lights purchased through Lowe's online. The mirror purchased at Pier 1. The shower tile feature is carrera marble patterned, and a sea grey tile purchased at 'The Tile Shop' in Urbandale, Iowa. The laminate wood floors are from Home Depot in Mushroom? or the next grayer color. The vanity is 60" dark grey with carrera marble top, sink, and faucet included. I changed the knobs. I think I ordered from Houzz but can't remember. It's also on Wayfair. It all looks better in person than in the photos. I don't love that the toilet is right in the middle as you open the door but I didn't want the hassle of changing the layout/footprint of the bathroom. Overall I am happy with my choices. The mirror is a little fancy to me but my husband loved it and the design echos the patterned shower tile so I went with it.

Yes dark blue/navy would be perfect. It can lean sophisticated or fun depending on accessories so it will be easy to age up as he grows.

@Sharon Hanes - current trends can quickly become outdated. That includes all of the gray which is going out and the white on white and white with navy that is the new trend. What makes something timeless that you won't tire of is picking colors that you love and incorporating those colors into your design. Neutrals are viewed as safe - no one walking into your home should be completely turned off by a neutral palette. For resale, most realtors will recommend a neutral palette. I sold my home in 3 days with a palette that included deep wine reds and deep smoky blue greens during a time when the average market time was about a month. I only needed one buyer who loved color and there was a ton of inventory that was builders beige and white or gray and white. Pick colors for your home that make your heart sing. If you walked into Macy's or Bed Bath and Beyond and didn't have to match the towels to any space - just needed towels and a shower curtain that was going to make you happy, what color would you pick? Once you answer that question figure out what color vanity you should use to make the color choices you love feel right in the space.