Hi @Jack ,
Welcome to Microsoft Q&A!
It isn’t currently supported to change the background of the error and warning squiggle.
For your requirement, you could report it to product team engineers by selecting “Help” menu > Send Feedback > Suggest a Feedback….
Thank you for helping us build a better Visual Studio!
- If the answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.