I've noticed this for years now and i' ve looked on this forum and found nothing about that.
When i first open a video there is a predominant blue colour, if i let mpc open with this video and opening it one more time with MPC then it hasn't this predominance.
It is clearly visible as i have 2 MPC opened with this video (i don't know if i can post screen captures here to show you?).
I always have to open twice a file to have correct colours.