Q:

why all visual studio 2013 code are with red background?

I have resharper installed and I'm not sure at this point whether it is resharper or VS?!

A:

Have you run tests with code coverage enabled? ReSharper/dotCover will highlight covered code in green, and uncovered code in red. You can disable this in the "coverage" tab of the Unit Test Sessions window. Check the toolbar buttons. You should also be able to click "Disable code highlighting" in the ReSharper → Cover menu.

