Hi Paul,
Thanks for contacting Syncfusion support.
We have checked your query. Based on your provided details, we suspect that reported issue may occurs due to overriding the background color for dialog’s content. By default, dialog background color would be #fff (white) only. So, we are not able to reproduce the issue in our end.
Could you please check whether any CSS styles overrides background color of dialog’s content element? Remove the styles, if any styles override from your application end.
For your convenience, we have prepared the sample in the below link.
Please modify the above sample by apply the CSS styles which you used in your application and share the modified sample to replicate the issue in our end. Otherwise share the CSS styles alone to replicate the issue in our end. It will help us to provide solution with other possible way.
Please let us know if you need further assistance on this.
Regards,
Rajendran R