Hi Ryan,
Thanks for your interest in Syncfusion Components.
We were able to render our report viewer control on “Dark” system color mode without any problem. Please refer the below attached snap for more details.
We suspect that the issue raised due to different theme other than default machine theme, please share the details of theme that you are using in your machine. It will be helpful for us to validate the problem at our end.
Regards,
Vinoth S.