There appears to be an issue when using a custom hovertemplate with heatmaps on certain themes. If using the extra tag, the text is almost impossible to see when using the “plotly_dark” template. Example below:
So far, I’ve tried modifying all the hoverinfo properties but this only affects the aspects of the hovertemplate not contained in the extra tag. In my example that would be the “Mileage: 28” as shown below:
I also tried modifying the color using a span tag as detailed in this post, but just like above, it has no effect on anything inside the extra tag.
Typically, anything inside the extra tag matches the marker/line color of the trace you are hovering over, but I’m not sure how this applies to heatmaps. Is there anything else to try? Or this just a current limitation of the heatmap figures?