Why when I applied a paragraph style to a text the text is colored behind

I dont´know what I done but, after having done lots ot texts in inDesign cs6 in a mac OX lion, now when I applied paragraphs styles to a text the text is coloured behind. I saw the preferences and all is normaly done and the paragraphs style I applied are the same I had applied in other texts without this consequencies but now all the texts I have done before when I open now have the text colored behind.

I also woud know the good fonts for a ebook - all open type? all senserif? Minion pro is a good one

Excuse my bad english and thanks for who can answer me