Why are my text-boxes red framed and coloured?

That is simply the color assigned to the layer. It has nothing to do with this topic which is now a year and half old. I'm locking it to avoid any future confusion.

Hello!

Thank you for your answer!

My text boxes have no style and no attributes, e. g. the boxes are without filling colour and without strokes/lines.

But just in that moment I found the solution: I'll attach a screenshot. 

Main menue "Ansicht" -> "Extras" -> "zugewiesene Rahmen ausblenden"

Thank you for helping. 

Many greetings, Susanne

Dear Manan, thanks for responding! 

I am afraid, that is not the reason. When I switch to "preview" the document, these shades are gone. And they are not printed as well. I should have wrote this in my first post.

Many greetings, Susanne