I noticed that on my odroid xu4, too.

But as stated by @MegaTimX it would be an easy work around to make both image and video either black or white.

It would be more pleasing to the eye to have a black "boot" image imho. Most consoles use black or at least dark colors. Especially on LCD displays with a high brightness it looks generally better to display something dark rather then bright white.

@eb2016 savage reboots or poweroffs cause such side effects, it's not a matter of pricy usb key. There is no.auto fsck (the linux checkdisk) on recalbox (yet)