Hello,
Sorry to hear you are having issues. In Start11, if I remember correctly, you can not change the Start menu font color manually. You can change it automatically to black or white depend on your Windows theme mode Light or Dark.

If you set the menu to have custom background, that will also cause the font to change according to the color of the background. Dark custom background will most probably push the font to be white and vise versa.

Thank you.
Basj,
Stardock Community Assistant.