i don’t think this is accurate. the color gradient heatmap still works (and is improved since the new map tiles). the problem on the page noted in the original post is that it asks the map tiles to be generated in a single specific color, thereby losing the color gradient.
here’s a tile with default gradient colors:
http://api.inaturalist.org/v1/heatmap/3/2/3.png
here’s the same tile with a single color applied:
http://api.inaturalist.org/v1/heatmap/3/2/3.png?color=%23FF4500