Getting filled markers with slightly lighter fill

[holtgrewe]

First of all, thank you for this great library.

In the following, I would like to get the marker circles filled with a slightly lighter color (different opacity) as the stroke. The following picture gives an idea.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "width": 1000,
  "height": 300,
  "layer": [
    {
      "encoding": {
        "x": {
          "field": "pos",
          "type": "quantitative",
          "scale": {"domain": [41190000, 41282000]},
          "axis": {"grid": false}
        },
        "y": {
          "field": "clinsig",
          "type": "quantitative",
          "scale": {"domain": [-3, 3]},
          "axis": {
            "gridColor": {
              "condition": {"test": "datum.value === 0", "value": "black"},
              "value": "#ddd"
            }
          }
        },
        "color": {
          "field": "clinsig",
          "type": "nominal",
          "scale": {
            "domain": [-3, -2, -1, 0, 1, 2],
            "range": ["grey", "darkgreen", "green", "yellow", "orange", "darkred"]
          },
          "legend": null
        },
        "size": {"value": 100}
      },
      "mark": {
        "type": "circle",
        "opacity": 0.8
      }
    }
  ],
  "data": {
    "values": [
      {"pos": 41197708, "clinsig": 2},
      {"pos": 41228523, "clinsig": -2},
      {"pos": 41197694, "clinsig": -1},
      {"pos": 41256168, "clinsig": -2},
      {"pos": 41251812, "clinsig": -2},
      {"pos": 41223254, "clinsig": -2},
      {"pos": 41234473, "clinsig": 2}
   ],
    "name": "dataset"
  }
}

[mattijn]

You can use the fillOpacity' encoding channel in combination with fill and ‘stroke. See for more info this table https://vega.github.io/vega-lite/docs/encoding.html#mark-prop