Plots with colour dimensions need a legend

[benjeffery]

No description provided.

[benjeffery]

scatter: {
    displayName: 'Scatter',
    dimensions: ['horizontal', 'vertical', 'colour'],
    plotlyTraces: (data) => {
      let traces = {};
      if (data.horizontal || data.vertical) {
        for (let i = 0, end = (data.horizontal || data.vertical).length; i < end; ++i) {
          let colour = data.colour ? data.colour[i] : 'rgb(0,0,0)';
          if (!traces[colour]) {
            traces[colour] = {
              x: [],
              y: [],
              marker: {
                color: colour,
              },
              type: 'scatter',
              mode: 'markers'
            };
          }
          if (data.horizontal)
            traces[colour].x.push(data.horizontal[i]);
          if (data.vertical)
          traces[colour].y.push(data.vertical[i]);
        }
      }
      return _values(traces);
    }
  }

Works for categoricals at least... for numerical you just need showscale.