tag lightens abbreviations in email sent to "followers" of blog

We surround our abbreviations with the abbr tag on all our posts. One of our followers notified us that the abbreviations in the email notices they receive are lighter in shade and harder to read. I know that this is for the auto readers– the text is usually highlighted with a color and a string of dots beneath the abbreviation.

My questions is can I control the shade or color of the highlighted abbreviation in the email sent out to the follower in CSS or is this something out of my control? I would like to make the shade darker or highlight it in a different color that is easier to see.

My site: https://www.hawaii.edu/news