I use the red version and it seems readable to me but yeah its dark... I'm not sure how to get it changed; you'll have to compare the fdb-blue folder with base and blanco folders to see which one has the app background for user guide app. Of course this depends on whether such a folder exists; it could simply be using the default app background of the theme in which case you'll have to make a new background and put it in the user guide app and try if it works out or not...