Using a colorful mushaf, is this permissible?
Decorating the mushaf through coloring it with different colors or using bright colors as separators to identify different chapters, juz’ etc. is perfectly permissible as it makes it easier for the reciter to identify chapters. In addition, it is highly recommended to beautify the mushaf and to treat it with the utmost respect due to its divine value of containing the words of God the Almighty.
Muslims throughout history have exerted their efforts in refining Arabic calligraphy with the purpose of beautifying and embellishing God’s divine words and thus permissibility is maintained on coloring the mushaf.
God the Almighty knows best.