Dear SidBream,
Welcome to Microsoft Community.
According to your description, the text color of your Hotmail account has changed from black to blue. We are sorry for the inconvenience this has caused you.
First of all, I want to explain to you that whether you subscribe to Microsoft 365 or not, Microsoft will not modify the user's email text color without authorization, and the email text color is synchronized with the sender, and I did not find the relevant Settings in classic Outlook to modify the email text color. If it is convenient for you, you can first provide me with relevant screenshots. Thank you for your patience and understanding.
In addition, you can also contact Microsoft's online support staff to ask for help, you can click on this link and follow the step-by-step instructions below to contact them. Contact - Microsoft Support
1). First, enter "Office" in the search box and then click "Get help" then click "Sign in to contact support" at the bottom of the page.
2). Currently logged in to another valid Microsoft account. (Please make sure you sign in with your personal Microsoft account, not your work and school account, or you won't see option 3、4、5.)
3). Under "Products & Services", select "Microsoft 365 and Office".
4). Under Category, select "Technical Support" and then click Confirm.
5). Click Chat with a support agent in your web browser.
Please contact Microsoft online support staff during business hours.
I hope this information has been helpful. If you have any questions, please let me know and I will be happy to help you further.
Have a good day.
Best Regards,
Jim - MSFT | Microsoft Community Support Specialist