How to make a selection in the colorbar of an altair plot?

Recently, I started using Altair and liked it a lot. However, I stumbled across something I could not figure out using the docs:

I have a scatter plot that encodes some continuous data as color. Is there a way of selecting a range of these values via the colorbar? Similar to how it is possible to select discrete features in a clickable legend.

I tried the following code:

cars = data.cars()
colorbar_brush = alt.selection_interval(fields=["Acceleration"], bind="legend")

chart = alt.Chart(cars).mark_circle().encode(
    x="Horsepower",
    y="Miles_per_Gallon",
    color=alt.condition(colorbar_brush, "Acceleration:Q", alt.value("lightgray")),
).add_params(
    colorbar_brush,
)

I also tried

colorbar_brush = alt.selection_interval(encodings=["color"], bind="legend")

Both did not work.

Alternatively, it is possible to use separate charts as clickable legends. But how could I create a chart of a color gradient?

As @joelostblom mentioned in his comment you can use a second plot to generate a color scale with a selection interval. I have implemented this using a mark_tick with good results.

Most of the options for the scale chart's y encoding are only for aesthetics and can be removed / tweaked as desired.

cars = data.cars()

color_encoding = alt.Color("Acceleration:Q", legend=None)
selection = alt.selection_interval(encodings=["y"])

chart = (
    alt.Chart(cars)
    .mark_circle()
    .encode(
        x="Horsepower",
        y="Miles_per_Gallon",
        color=alt.condition(selection, color_encoding, alt.ColorValue("lightgray")),
    )
)

legend_chart = (
    alt.Chart(
        alt.sequence(
            min(cars.Acceleration), max(cars.Acceleration), 0.01, as_="Acceleration"
        )
    )
    .mark_tick(orient="horizontal")
    .encode(
        y=alt.Y(
            "Acceleration:Q",
            axis=alt.Axis(
                orient="right",
                ticks=False,
                grid=False,
                titleAngle=0,
                titleAnchor="end",
                titleAlign="center",
                titleBaseline="bottom",
                titleY=-10,
                tickCount=3
            ),
        ).scale(zero=False, padding=0),
        color=color_encoding,
    )
).add_params(selection)

chart | legend_chart