Actually, the Problems by severity widget shows the same color despite there is any problem or not. There is no possibility to change the color ("light-off") of severity boxes which have zero problems.

The solution is quite simple - add a CSS class (e.g. "no-problem") to the div element with zero problems in the given severity:

<div class="disaster-bg"><span class="count">0</span> Disaster</div>

would become

<div class="disaster-bg no-problem"><span class="count">0</span> Disaster</div>

Then we can add this CSS code to a template:

.no-problem {
  opacity: 0.2;
}

I've attached a simulation of how it could have looked.