Dear Julia Murta Rietra Dias,
Good day! Thank you for contributing to the Microsoft Community.
I understand your query here. However, to better understand your query and provide accurate information, May I please double confirm if the solid colors are removed in manage color categories as well? If you haven't check it yet, go to your calendar items -->right click on the items -->Manage color categories -->Select your account -->click on the plus sign at the bottom (+) --> give name for the new categories -->Then, check if you can able to create new color categories with solid color.
- Could you please provide us with the screenshot of the manage categories color options?
I look forward to your response. Kindly note that the above requested information is required for further analysis and troubleshooting of your situation. Your patience and cooperation are much appreciated.
Thanks for your precious time. Have a nice day!
Sincerely,
Microsoft Community Moderator