Why does a grey screeen show up when I start my MacBook

Which version of OS X or macOS is your MacBook running? Which exact model is your MacBook? Using the following reference article, at what point in the startup process does the screen appear grey and for how long?

About the screens you see when your Mac starts up - Apple Support

I have the same thing... just pink screen for 2 seconds. Apple engineering team has no idea what is it

Please start your own post. It is very unlikely that your pink screen issue is any way related to the OP's grey screen issue.