Shalom, A person can use colored highlighter, or To mark With pen or pencil over a word in printed Hebrew books (talmud, Shulchan Arukh, Chumash, tanakh)?
thank you for your question.
It i permitted to mark up a sefer in a way that helps the person’s learning. for example, highlighting key words that one want to remember is permitted. It is not disrespectful to the sefer since it is helping the person remember his learning.