Assalamu alaikom, I bought some designs for uncolored bookmarks that I am free to print any number of copies of and use personally, as long as i dont resell those printed copies for profit. However, if i color and decorate those copies, meaning that i would change those designs with my own effort and ideas, can I sell them and charge money for the effort i did? or would it be haram?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the change that you want to make to those bookmarks render them out of their original state, then there is nothing wrong in selling them and benefitting from them.

It is the specialists in the field who estimate whether or not they are in their original state (after the changes). and (whether or not these changes) invalidate the right of their owners.

Therefore, if the coloring and changing the designs would not make the owners lose their right in them, and they have only authorized you to use them for your personal usage without earning from them, then it is not permissible to violate their condition. Muslims should honor their conditions.

Allah knows best.