Great question! Let's break this down and fix that frustrating legend color mismatch issue you're seeing with your WPF LiveCharts implementation.

Root Cause of the Mismatch #

The core problem here is that you're using CandleSeries—a component designed for stock candlestick charts—to render box plots. CandleSeries has built-in color logic tied to "up" vs "down" candlestick movements (using FillUp/FillDown properties), while your code is repurposing it to draw box plot quartiles. This mismatch in intended use causes the legend to pick up a default color that doesn't align with the box plot visuals you're rendering.

Fix 1: Use LiveCharts' Native BoxPlotSeries (Recommended) #

LiveCharts provides a dedicated BoxPlotSeries component built specifically for box plot visuals, and it handles legend color synchronization out of the box. Here's how to rewrite your AddBoxplotSeries method to use the correct component:

public void AddBoxplotSeries(List<KeyValuePair<string, List<double>>> data, string title)
{
    CartesianVisibility = Visibility.Visible;
    var boxPlotSeries = new BoxPlotSeries
    {
        Title = title,
        Values = new ChartValues<BoxPlotData>()
    };

    string[] labels = new string[data.Count];

    foreach (var item in data)
    {
        var stats = item.Value;
        // Use LiveCharts' native BoxPlotData to encapsulate quartile stats
        var boxPlotData = new BoxPlotData(
            minimum: stats.Minimum(),
            lowerQuartile: stats.LowerQuartile(),
            median: stats.Median(),
            upperQuartile: stats.UpperQuartile(),
            maximum: stats.Maximum()
        );
        boxPlotSeries.Values.Add(boxPlotData);
        labels[data.IndexOf(item)] = item.Key;
    }

    CartesianSeries.Add(boxPlotSeries);
    XAxisLabels = labels;
    LabelFormatter = value => value.ToString("N");
}

This approach ensures the legend color automatically matches the box plot's stroke/fill properties, since BoxPlotSeries is designed to sync these elements by default.

Fix 2: Manually Sync Colors If You Must Use CandleSeries #

If you have a specific reason to stick with CandleSeries, you can override its default color logic to force consistency between the chart and legend:

public void AddBoxplotSeries(List<KeyValuePair<string, List<double>>> data, string title)
{
    CartesianVisibility = Visibility.Visible;
    ChartValues<OhlcPoint> values = new ChartValues<OhlcPoint>();
    string[] labels = new string[data.Count];

    foreach (var item in data)
    {
        double[] ohlc = new double[4];
        ohlc[0] = item.Value.LowerQuartile();
        ohlc[1] = item.Value.Maximum();
        ohlc[2] = item.Value.Minimum();
        ohlc[3] = item.Value.UpperQuartile();
        labels[data.IndexOf(item)] = item.Key;
        values.Add(new OhlcPoint(ohlc[0], ohlc[1], ohlc[2], ohlc[3]));
    }

    // Force uniform colors to sync legend and chart visuals
    var candleSeries = new CandleSeries() 
    { 
        Values = values, 
        Title = title,
        Fill = Brushes.SteelBlue,
        Stroke = Brushes.DarkSlateGray,
        FillUp = Brushes.SteelBlue,
        FillDown = Brushes.SteelBlue,
        StrokeUp = Brushes.DarkSlateGray,
        StrokeDown = Brushes.DarkSlateGray
    };
    CartesianSeries.Add(candleSeries);
    XAxisLabels = labels;
    LabelFormatter = value => value.ToString("N");
}

By setting identical colors for both "up" and "down" states, you eliminate the color discrepancy between the legend and your repurposed box plot candles.

Why This Happens in Minimal Apps #

This issue persists in your test app because it's not a bug in your logic—it's a mismatch between the component's intended use and how you're using it. CandleSeries never expects to be used as a box plot tool, so its default legend color behavior doesn't account for your use case.

内容的提问来源于stack exchange，提问作者Thor Giversen