Can't see weight paint heatmap in blender 2.8 release candidate. What should I do to toggle it? I am trying to weight paint a terrain to adjust the amount of stones in some spots, but when I go in weight paint mode the heatmap is not showing, even if there are changes on the stones distribution when I paint.

Is there an option to toggle or another way to show it?

Thank you
You can now pick weight painting heat map opacity, but for some reason it defaults to zero with some previously saved projects (probably because the category didn't exist before now). 

Hope this fixes your problem.