I know this is a necro-post but I've got something really useful to add here, which is simple and pretty helpful.
If you want your screen black at the start of the game just change it with a tint screen. The problem with it flashing for a second is that you need to change the time.
Default is 60 frames which is 1 second. If you change it to 1 then it's pretty much instant, be sure to check wait for completion. Put this in a parallel process and the first thing in the event.
Sorry if I'm understanding the problem wrong, but if I'm not, it'd be really helpful since everyone is completely overlooking this.