It's fairly hard to find a perfect setting, as highlighted letters in Word are easier to see using a light highlight colour, while the Excel cursor is easier to see using a dark colour. The highlight colour settings can be changed to anything you want, but you will need to restart the Office application to see the changes. The settings for all highlight settings in Office X are controlled by the System Preferences -> General option. After a colleague complained about the same problem, I went scouting to see if this setting could be changed. I've been finding the cursor (cell highlighter) in Excel vX quite hard to see (very soft blue).
