When viewing a report, some users face the issue that all the lines for line chart are presented in black color/ for bar chart the columns are shown as stripped colors.
This is configured on the instance as per Accessibility standards. The Now Platform is designed to be as accessible as possible without user modification or setting changes. There are several colour and style changes that make the platform more accessible.
If the above is not required, you can disable the 'Data Visualisation Pattern'. By default in OOB, this is set disabled.
Data Visualization Pattern toggle button can be found from the top level settings (the Gear icon at the top right ) > General.
The above step updates the user preference for the user to glide.ui.report.accessibility.patterns to false. By default, this is set to true. So, to disable this user preference for all users, it can be false, and System checkbox should be checked.
Click here for more information accessibility and compliance on the ServiceNow platform.
Click here for more information about the system settings for the user interface (UI).