如何在双轴图表中显示/添加图例？

我创建了一个双轴图表，我在同一个图表中绘制到达时间和离开时间，并将记录数的总和显示为行。

默认情况下，Tableau 将“度量名称”添加到我的每一列“标记”中，我会得到一个自动图例，以一种颜色显示“记录数”。

然而，这根本没有用......

I want each time variable (eg. arrival time) to show up in a different colour. The only way I have been able to do this is by removing the "Measure Names" pill from the Marks card and then setting each axis to have its own colour. But as soon as I do this, the Legend disappears and now I finally get a nice graph with a line in each colour, but no legend to show what line is assigned to what colour.

Also the Legend option gets disabled when I use this layout.

How can I add the Legend to this?

Please note that the solution in this post doesn't help to answer this question.