Updated FAQ

FAQ.md

@@ -3515,6 +3515,9 @@ Message classification is a pro feature, except for the spam folder.
 Unfortunately, Android [does not support](https://stackoverflow.com/a/26511725/1794097) dynamic themes,
 which means all themes need [to be predefined](https://github.com/M66B/FairEmail/blob/master/app/src/main/res/values/styles.xml).
 
+Since for each theme there needs to be a light, dark and black variant,
+it is not feasible to add for each color combination (literally millions) a predefined theme.
+
 Moreover, a theme is more than just a few colors.
 For example themes with a yellow accent color use a darker link color for enough contrast.