Would could be the reason for Coloured stuff on the screen shutting of

I have just exchanged the display of my MBP under an authorized service a couple of weeks ago. (service done is still under warranty).

I have been noticing that the screen once I shut down, actually the moment it shuts down, for a fraction of a second, there are some weird colours on the screen. The whole screen flashes very quickly on this colours and shuts down.

During the use there is glitching, or weird things, just at this single moment of shutting down the mbp.

Anyone with this experience? It does not hurt at all, but it could be something related to this service done recently, or something that could build up in the future.

Thanks in advance to all =)