I get Flashed everytime I change pages

Site URL: https://cornet-bellflower-9gbs.squarespace.com/

Hey,

Im working on a website with some friends and right now im having the problem that my Black website flashbangs me everytime i change to a different subdomain. Im not sure how i can get rid of this because i already checked all the Colours in "Design" and it seems there is no way for me to change the colour of the Base page (not sure if that makes sense.) I also have added a video where you can see what i mean.

Password for the Website is: Peter 

(dont ask why)

Thank you :)

 

It takes a half second to load the black background color. The site would flash if the solid bacground were white, you just wouldn't see it.