Fill

<div id="diagram"></div>
<script>
  $("#diagram").kendoDiagram({
    shapes: [{
      visual: function() {
        var group = new kendo.dataviz.diagram.Group();
        group.append(new kendo.dataviz.diagram.Path({
          data: "M 80 0 C 100 0 100 0 100 20 L 100 80 C 100 100 100 100 80 100 L 20 100 C 0 100 0 100 0 80 L 0 20 C 0 0 0 0 20 0Z",
          fill: {
            color: "red",
            opacity: 0.7
          }
        }));
        return group;
      }
    }]
  });
</script>

<div id="diagram"></div>
<script>
  $("#diagram").kendoDiagram({
    shapes: [{
      visual: function() {
        var group = new kendo.dataviz.diagram.Group();
        group.append(new kendo.dataviz.diagram.Path({
          data: "M 80 0 C 100 0 100 0 100 20 L 100 80 C 100 100 100 100 80 100 L 20 100 C 0 100 0 100 0 80 L 0 20 C 0 0 0 0 20 0Z",
          fill: {
            color: "#ff6600"
          }
        }));
        return group;
      }
    }]
  });
</script>

<div id="diagram"></div>
<script>
  $("#diagram").kendoDiagram({
    shapes: [{
      visual: function() {
        var group = new kendo.dataviz.diagram.Group();
        group.append(new kendo.dataviz.diagram.Path({
          data: "M 80 0 C 100 0 100 0 100 20 L 100 80 C 100 100 100 100 80 100 L 20 100 C 0 100 0 100 0 80 L 0 20 C 0 0 0 0 20 0Z",
          fill: {
            gradient: {
              type: "linear",
              start: [0, 0],
              end: [1, 1],
              stops: [
                { offset: 0, color: "red" },
                { offset: 1, color: "blue" }
              ]
            }
          }
        }));
        return group;
      }
    }]
  });
</script>

<div id="diagram"></div>
<script>
  $("#diagram").kendoDiagram({
    shapes: [{
      visual: function() {
        var group = new kendo.dataviz.diagram.Group();
        group.append(new kendo.dataviz.diagram.Path({
          data: "M 80 0 C 100 0 100 0 100 20 L 100 80 C 100 100 100 100 80 100 L 20 100 C 0 100 0 100 0 80 L 0 20 C 0 0 0 0 20 0Z",
          fill: {
            color: "red",
            opacity: 0.3
          }
        }));
        return group;
      }
    }]
  });
</script>