Please consider adding "Al-Wadeh Fi At-Tajweed" Mushaf (مصحف الواضح في التجويد) to the app or try to re-create a Mushaf with a similar idea.
Another Mushaf that shares the same idea of the mentioned one above is "Muallim At-Tarteel" (مصحف معلم الترتيل) but the images of the pages I have found are not very clear.
This is another method to practice Tajweed instead of using the color coded letters method which may be frustrating or hard to distinguish for a certain group of users, for that reason I suggest that you implement the proposed technique in the web version of your app as well if possible.
Asslamu Alaykom!
Please consider adding "Al-Wadeh Fi At-Tajweed" Mushaf (مصحف الواضح في التجويد) to the app or try to re-create a Mushaf with a similar idea.
Another Mushaf that shares the same idea of the mentioned one above is "Muallim At-Tarteel" (مصحف معلم الترتيل) but the images of the pages I have found are not very clear.
This is another method to practice Tajweed instead of using the color coded letters method which may be frustrating or hard to distinguish for a certain group of users, for that reason I suggest that you implement the proposed technique in the web version of your app as well if possible.
Jazakum Allah Khayra for all of your efforts.