The styles used on the Pagure heatmap are so light colored at the light usage level that they're practically invisible unless you have a really well tuned display (and really good eyes). The scale should start darker to be easier to use for people with normal (or worse) eyes.
Metadata Update from @ryanlerch: - Issue assigned to ryanlerch
Metadata Update from @ryanlerch: - Issue set to the milestone: 5.2
Metadata Update from @ryanlerch: - Issue tagged with: UI
Commit e329e97a fixes this issue