As luck would have it, I just answered this exact question from somebody else only a couple of days ago 
What does the Blue/Grey Striped Background of an action signify?
To repeat my answer from there: That's KM8's new way of showing you that an action contains the text that you're searching for in the KM editor's search field:
Just make sure there's no text in that field and this e̶f̶f̶e̶c̶t̶ background should go away.