Try this...
1. inside of your playable scenes create an
at begin of scene action (if you don't already have one).
2. add an execute a script action part containing (see code block below) to the very top of the at begin of scene actions action part list...
game.CurrentScene.SceneBrightness = 0
game.CurrentScene:to(500, {SceneBrightness = 100}, easeQuintInOut)
It should set the scenes brightness to 0 (which will be full black) on scene load & then should fade back to 100% over 500ms.
P.S: I can't guarantee it will work in the current public build, but it will work in the next public build. I don't know when the next build will be out though. If it doesn't work, it might work if you link directly to the scene itself rather than trying to access it via game.CurrentScene.
-- replace scene name with the name of the scene (name is case sensitive)
Scenes["scene_name"].SceneBrightness = 0
Scenes["scene_name"]:to(500, {SceneBrightness = 100}, easeQuintInOut)