Conditions in color encodings are not reflected in legend

[rlm1023]

Bug Description

If you have a color encoding with a conditional re-coloring on it for particular values, those re-colorings are not reflected in the legend.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"url": "data/cars.json"},
  "mark": "point",
  "encoding": {
    "x": {"field": "Horsepower", "type": "quantitative"},
    "y": {"field": "Miles_per_Gallon", "type": "quantitative"},
    "color": {
      "field": "Origin",
      "type": "nominal",
      "condition": {"test": "datum['Origin'] === 'USA'", "value": "red"},
      "scale": {"scheme": "category10"}
    }
  }
}

Produces:

Repro

Checklist

• I checked for duplicate issues.