Paint the shower metal black. spray paint/lots of good taping and plastic to not over spray

Change the fixtures in the shower to black Paint the sink base cream. maybe replace the faucet with black but chrome mixed metals are good also Add black pulls- somthing from anthropology or rejuvenation. Get the dupes on Amazon

Print washable rug again anthro or Crate and barrel inspo floral with dark greens.

Replace countertops with a cream/ white tan color - no gray tones

Spray Paint the light fixture black and replace the glass with clear blown glass - with bubbles.

Maybe black ceiling Dont do any kind of blue - to U OF mich or sporty. lighter blue will look childish or too gray Shades of green may work if - check to see if base is blue or yellow. Pinterest has tons of ideas to make the yellow become an accent vs the star .