/system/coverage/browser/CodeBrowser.cfc creates HTML/JavaScript content. In that content it creates a variable named lineNumbersBGColorsJSON. This is currently set as follows.
The resulting file typically looks something like this:
When the Prefix serialized JSON with box is checked in ACF (we are running ACF 2018) the result ends up as follows:
The prefix comments out the JSON string, causing the line numbers not to show the colors.
Here is the report with no line colors:
After the fix it looks correct.
Pull Request 114 has been opened