Changing flashes look plz help

my problem is…
when you make a new doc it has a 550x400 works space i belive and its white well great we can change the canvas color
but the gray stuff the workspace around it is there a way to change it ???
because it is hard to work with most of my map in the game im making is gray road … can i change it and how? somthing like bright green or bright purple or somthing weird