Here is a color palette based on your request for all 12 colors of the rainbow, with lighter and darker shades for each color:

json
{
  "palette_name": "Gentle Rainbow",
  "colors": [
    {
      "name": "Light Red",
      "hex_code": "
          
          #FF7F7F
       "
    },
    {
      "name": "Red",
      "hex_code": "
          
          #FF4C4C
       "
    },
    {
      "name": "Dark Red",
      "hex_code": "
          
          #BF0000
       "
    },
    {
      "name": "Light Orange",
      "hex_code": "
          
          #FFA07A
       "
    },
    {
      "name": "Orange",
      "hex_code": "
          
          #FF8C00
       "
    },
    {
      "name": "Dark Orange",
      "hex_code": "
          
          #BF5C00
       "
    },
    {
      "name": "Light Yellow",
      "hex_code": "
          
          #FFFFB3
       "
    },
    {
      "name": "Yellow",
      "hex_code": "
          
          #FFFF00
       "
    },
    {
      "name": "Dark Yellow",
      "hex_code": "
          
          #BFBF00
       "
    },
    {
      "name": "Light Green",
      "hex_code": "
          
          #B2FF99
       "
    },
    {
      "name": "Green",
      "hex_code": "
          
          #4CFF00
       "
    },
    {
      "name": "Dark Green",
      "hex_code": "
          
          #008000
       "
    },
    {
      "name": "Light Blue",
      "hex_code": "
          
          #99CCFF
       "
    },
    {
      "name": "Blue",
      "hex_code": "
          
          #007FFF
       "
    },
    {
      "name": "Dark Blue",
      "hex_code": "
          
          #003D99
       "
    },
    {
      "name": "Light Indigo",
      "hex_code": "
          
          #A8A0FF
       "
    },
    {
      "name": "Indigo",
      "hex_code": "
          
          #4B0082
       "
    },
    {
      "name": "Dark Indigo",
      "hex_code": "
          
          #2E005D
       "
    },
    {
      "name": "Light Violet",
      "hex_code": "
          
          #D1A6FF
       "
    },
    {
      "name": "Violet",
      "hex_code": "
          
          #8A2BE2
       "
    },
    {
      "name": "Dark Violet",
      "hex_code": "
          
          #5B2E91
       "
    }
  ]
}

This palette features a range of shades for each of the 12 colors of the rainbow, transitioning from light to dark tones to create a gentle and harmonious visual experience.

Would you like to explore any specific colors further or seek additional palettes?