You can target just the site title by including the ID in the selector:
I set all three pseudoclasses (I left out active) to the same color, because most sites don't have their site titles changing color on hover. If the theme has a Custom CSS option, then add the above rule to that field. If it doesn't, use a CSS plugin.
What's weird about this theme is that the style.css file uses the British spelling of the word colour instead of color, so all of the CSS rules which uses that property aren't working.