How to customize the grouped list view background color

Learn2Live I haven't checked the difference between your JSON code and mine, but my code is shown below:

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",
  "groupProps": {
    "hideFooter": true,
    "headerFormatter": {
      "elmType": "div",
      "style": {
        "flex-wrap": "wrap",
        "display": "flex",
        "box-sizing": "border-box",
        "padding": "4px 8px 5px 8px",
        "border-radius": "6px",
        "align-items": "center",
        "white-space": "nowrap",
        "overflow": "hidden",
        "margin": "1px 4px 4px 1px",
        "background-color": "#ffbf00"
      },
      "children": [
        {
          "elmType": "span",
          "attributes": {
            "iconName": "Link"
          },
          "style": {
            "max-width": "24px",
            "max-height": "24px",
            "margin-top": "2px",
            "border-radius": "2px"
          }
        },
        {
          "elmType": "div",
          "children": [
            {
              "elmType": "div",
              "style": {
                "display": "flex",
                "flex-direction": "row",
                "justify-content": "center"
              },
              "children": [
                {
                  "elmType": "div",
                  "txtContent": "=  @group.count",
                  "style": {
                    "padding": "5px 5px 5px 5px",
                    "font-weight": "500"
                  }
                }
              ]
            }
          ]
        },
        {
          "elmType": "div",
          "children": [
            {
              "elmType": "div",
              "style": {
                "display": "flex",
                "flex-direction": "row",
                "justify-content": "center"
              },
              "children": [
                {
                  "elmType": "div",
                  "txtContent": "=  @group.fieldData.displayValue +' links  ' ",
                  "style": {
                    "padding": " ",
                    "font-weight": "500"
                  }
                }
              ]
            }
          ]
        }
      ]
    }
  }
}

Rob
Los Gallardos
Microsoft Power Automate Community Super User.
Principal Consultant, SharePoint and Power Platform WSP Global (and classic 1967 Morris Traveller driver)