Hi Stephen Pruitt,
Based on your description, this issue typically occurs when a theme is actively applied, as themes can override manual background changes and force the desktop to revert to a picture. To fix this, please try going to Settings > Personalization > Themes and switch to the Windows (Light) or Windows (Default) theme before choosing a solid color. After that, go back to Personalization > Background and set the Background option to Solid color again.
If the issue persists, you may also want to check whether any third-party customization tools are installed, as these applications can enforce background settings. Additionally, ensure that your system is not syncing a theme from your Microsoft account by going to Settings > Accounts > Windows backup and turning off theme sync if enabled. Once those settings are adjusted, your chosen solid color should remain applied without reverting to an image.
Please "accept the answer" so that it could be spread further to those in need too. If not, is there anything I can help you with? Please let me know.