axisstylex.vl

{
    "config": {
        "style": {
            "x-style": {
                "domainColor": "orange",
                "labelExpr": "if (datum.value <= 100, 'low:' + datum.label, 'high:' + datum.label)",
                "gridColor": "lightgreen"
            }
        }
    },
    "mark": "point",
    "data": {
        "url": "https://vega.github.io/vega-lite/data/cars.json"
    },
    "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
    "encoding": {
        "color": {
            "field": "Origin",
            "type": "nominal",
            "legend": null
        },
        "x": {
            "field": "Horsepower",
            "type": "quantitative",
            "axis": {
                "style": "x-style"
            }
        },
        "y": {
            "field": "Miles_per_Gallon",
            "type": "quantitative"
        }
    }
}