Here is a color palette based on your request for a warm mustard yellow, terracotta brick or peach red, and an olive green to complement your millennial grey room.

json
{
  "palette_name": "Warm Earthy Tones",
  "colors": [
    {
      "name": "Mustard Yellow",
      "hex_code": "
          
          #D9A300
       "
    },
    {
      "name": "Terracotta Brick",
      "hex_code": "
          
          #C65D3D
       "
    },
    {
      "name": "Peach Red",
      "hex_code": "
          
          #FF6F61
       "
    },
    {
      "name": "Olive Green",
      "hex_code": "
          
          #6B8E23
       "
    }
  ]
}

This palette combines warm, earthy tones that will create a cozy and inviting atmosphere in your grey room. The mustard yellow adds warmth, while the terracotta and peach red bring in a rustic charm, and the olive green adds a touch of nature.

Would you like suggestions on how to use these colors in your room decor, or do you need help with anything else?