Json 无法根据vega规范中的条件设置文本 colored颜色

我已经try 了ChatGPT提出的所有建议以及我能想到的每一种变体，以使以下规范发挥作用，以便文本值将改变图表顶部的 colored颜色 . 如果您使用vega数据查看工具，您可以看到 for each 日期定义了价格/预算值，您还可以将一个或所有值显示为文本，但无论默认 colored颜色 是什么，文本始终是彩色的(本例中为蓝色) 即使使用1=1也无法正确计算.

idea ？

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "Monthly stock prices of a Tech Company.",
  "background": "white",
  "padding": 5,
  "width": 400,
  "height": 200,
  "data": [
    {
      "name": "source_0",
      "values": [
        {"date": "2021-01-01", "symbol": "AAPL", "price": 150, "budget": 110},
        {"date": "2021-02-01", "symbol": "AAPL", "price": 100, "budget": 50},
        {"date": "2022-03-01", "symbol": "AAPL", "price": 90, "budget": 90},
        {"date": "2022-04-01", "symbol": "AAPL", "price": 130, "budget": 150}
      ],
      "transform": [
        {
          "type": "filter",
          "expr": "datum.symbol === 'AAPL'"
        },
        {
          "type": "formula",
          "expr": "slice(datum.date, 0, 7)",
          "as": "year_month"
        }
        ,
        {
          "type": "formula",
            "expr": "(datum.price>=datum.budget) ? 1 : 0"
            ,"as":"isgreen"
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "band",
      "domain": {"data": "source_0", "field": "year_month"},
      "range": "width",
      "padding": 0.1
    },
    {
      "name": "y",
      "type": "linear",
      "domain": [0, 200],
      "range": [200, 0],
      "nice": true
    }
  ],
  "axes": [
    {
      "scale": "x",
      "orient": "bottom",
      "title": "Month"
    },
    {
      "scale": "y",
      "orient": "left",
      "title": "Price ($)"
    }
  ],
  "marks": [
    {
      "type": "text",
      "from": {"data": "source_0"},
      "encode": {
        "enter": {
          "x": {"scale": "x", "field": "year_month", "band": 0.5},
          "y": {"scale": "y", "field": "budget"},
         "text": {"field":"budget"},
          "align": {"value": "center"},
          "baseline": {"value": "middle"} 
           , "fill": {
          "condition": {
            "test": "1=1",
            "value": "green"
          },
          "value": "blue"
        }

        
      }
      }
    }
  ]
}