Revit :: Rendered Images Eventually Turn Blue?

I recently opened a project I worked on months ago and noticed certain materials in my rendered images had turned blue. I created a new rendering in which all materials came out great and I saved it. Minutes later I opened the new rendering and it too became blue. I worked on this project for months and have not made any changes to materials. All previously saved images in my file, the wall materials, stairs, and certain furniture have all turned blue.