Vega-Lite渐变：如何让颜色断点与Y轴刻度关联？

我有一个指标，希望在面积图中根据该指标在不同时间点的数值，按区间显示渐变颜色：良好（0至0.1=绿色）、一般（>0.1至0.3=黄色）、较差（>0.3=红色）。如何让颜色断点与Y轴的实际刻度相关联？

我原本以为可以通过offset指定颜色断点，初次尝试时显示正常：

{
  "width": 600,
  "data": {
    "values": [
      {
        "__row__": 0,
        "calendar_month_year": "Dec-23",
        "concentration_risk_monthly": 0.51
      },
      {
        "__row__": 1,
        "calendar_month_year": "Jan-24",
        "concentration_risk_monthly": 0.5
      },
      {
        "__row__": 2,
        "calendar_month_year": "Feb-24",
        "concentration_risk_monthly": 0.27
      },
      {
        "__row__": 3,
        "calendar_month_year": "Mar-24",
        "concentration_risk_monthly": 0.22
      },
      {
        "__row__": 4,
        "calendar_month_year": "Apr-24",
        "concentration_risk_monthly": 0.25
      },
      {
        "__row__": 5,
        "calendar_month_year": "May-24",
        "concentration_risk_monthly": 0.22
      }
    ]
  },
  "mark": {
    "type": "area",
    "color": {
      "x1": 1,
      "y1": 1,
      "x2": 1,
      "y2": 0,
      "gradient": "linear",
      "stops": [
        {"offset": 0, "color": "#00800166"},
        {"offset": 0.3, "color": "#F7B50066"},
        {"offset": 1, "color": "#A9281F66"}
      ]
    }
  },
  "encoding": {
    "x": {
      "field": "calendar_month_year",
      "type": "ordinal",
      "sort": {"field": "__row__"},
      "axis": {"title": null},
      "scale": {"padding": 0}
    },
    "y": {
      "field": "concentration_risk_monthly",
      "type": "quantitative",
      "axis": {"title": null}
    }
  }
}

效果如下：

但当我将所有指标数据改为低于0.05（远低于绿色阈值0.1）时：

{
  "width": 600,
  "data": {
    "values": [
      {
        "__row__": 0,
        "calendar_month_year": "Dec-23",
        "concentration_risk_monthly": 0.051
      },
      {
        "__row__": 1,
        "calendar_month_year": "Jan-24",
        "concentration_risk_monthly": 0.05
      },
      {
        "__row__": 2,
        "calendar_month_year": "Feb-24",
        "concentration_risk_monthly": 0.027
      },
      {
        "__row__": 3,
        "calendar_month_year": "Mar-24",
        "concentration_risk_monthly": 0.022
      },
      {
        "__row__": 4,
        "calendar_month_year": "Apr-24",
        "concentration_risk_monthly": 0.025
      },
      {
        "__row__": 5,
        "calendar_month_year": "May-24",
        "concentration_risk_monthly": 0.022
      }
    ]
  },
  "mark": {
    "type": "area",
    "color": {
      "x1": 1,
      "y1": 1,
      "x2": 1,
      "y2": 0,
      "gradient": "linear",
      "stops": [
        {"offset": 0.0, "color": "#00800166"},
        {"offset": 0.3, "color": "#F7B50066"},
        {"offset": 1.0, "color": "#A9281F66"}
      ]
    }
  },
  "encoding": {
    "x": {
      "field": "calendar_month_year",
      "type": "ordinal",
      "sort": {"field": "__row__"},
      "axis": {"title": null},
      "scale": {"padding": 0}
    },
    "y": {
      "field": "concentration_risk_monthly",
      "type": "quantitative",
      "axis": {"title": null}
    }
  }
}

我原本期望整个区域为绿色，但似乎offset是相对于整个绘图区域的，因此即使所有指标都低于0.1，仍会出现红色区域：

内容的提问来源于stack exchange，提问作者Tyler Rinker