Is it permissible to teach using a fluorescent pen or to underline the verses of the Noble Qur’an with a pen?

It is permissible to mark the verses of the Holy Quran for the purpose of memorization, observing their meaning, or for any other legitimate religious purpose, as long as it does not lead to an alteration of the Quran or mockery of it. This is because the Quran was revealed for reflection upon its meanings, and anything that aids in this is permissible. The early Muslims (Salaf) warned against adding anything that is not from the Quran to it, for fear of it becoming mixed with it. However, marking words for a legitimate religious purpose, which does not cause confusion with the Quran, is permissible.