Grey text in Kobo store book. Can I change?

I purchased a book in the Kobo store which appears to be using a custom font color. It's noticeably greyer than the normal black. Not a good idea for an ebook...

Is there any way to easily change this? I did install Calibre but couldn't see anything obvious.

Or is it a case of finding and editing a css file in the book on my Kobo device?

Thanks.