Based on your request for a color palette inspired by a typographic poster using Helvetica and Garamond with high to medium contrast and incorporating green, here is a suggested color palette:

json
{
  "palette_name": "Typographic Harmony",
  "colors": [
    {
      "name": "Forest Green",
      "hex_code": "
          
          #2E8B57
       "
    },
    {
      "name": "Charcoal Grey",
      "hex_code": "
          
          #333333
       "
    },
    {
      "name": "Light Cream",
      "hex_code": "
          
          #F5F5DC
       "
    }
  ]
}

This palette features a deep, rich green for a strong focal color, complemented by a dark charcoal for text and a soft cream to add contrast while keeping the overall look elegant and readable.

Would you like more options or assistance with how to apply this palette in your poster design?