Please upgrade to 2.3 here.
The 2.2 and earlier branches are no longer being updated.
Superhero panel headers - bad color
This discussion is related to the Bootstrap
So I discovered that in your custom_superhero css in panel headers you have color from un-themed Bootstrap.
EDIT: My pc is a bit slow so my GitHub client is lagging so I cannot create pull request, but enable superhero theme and look at discussions headings. It it #F5F5F5 color and it should be #485563