Here’s what Dictionary.com says about this trio:
Basically, insure, ensure, and assure mean to make a person or thing more sure. Insure should be restricted to providing or obtaining insurance to indemnify or guarantee someone or something against a loss. Ensure can be used in all other senses, especially ‘to make certain’. Ensure can also imply a guarantee. Then there is a third word, assure, which means to make a promise or convince. Assure also implies the removal of doubt and suspense within someone’s mind.
So in my post, either “ensure” or “assure” would have worked. Irregardless, for all intensive purposes, I assure you that the pain of making color copies was too much. Anyways, it’s all a mute point.