Blue pain on Macbook pro screws

Hello all. I have taken it upon myself to look under the hood of my Mac and while removing the outer screws, I noticed that each one had blue paint in the threads - in the process of unscrewing and screwing back in, I noticed the paint coming off. I am aware that opening up the machine will supposedly void the warranty, and I am just curious if that blue paint was provided as a means of detection. In other words, would a repair tech look at missing paint on the screws and know whether or not the machine had been opened? Perhaps silly, maybe paranoid, but curious minds want to know! Any thoughts?

Thank ya, thank ya!