If you open the advanced tab of the hyperlink editor, add text-decoration: none; color: #ddddd to the style postion. The text-decoration remove the underline and color will change the color. Just update the hex code to whatever color you would like to use.
There are some similar threads here:
The advanced tab in the hyperlink editor, doesn't seem to exist in the newest version of Marketo. Any pointers on how I access those settings in the new UI?