Let the area of the smaller square be 4x cm². Since the ratio of the areas of the two squares is 4:5, the area of the bigger square is 5x cm². Given that the area of the bigger square is 475 cm², we have 5x = 475. Dividing both sides of the equation by 5, we get x = 475/5 = 95. Therefore, the area of the smaller square is 4x = 4(95) = 380 cm². The total ratio of both squares is 4x:5x = 380:475 = 76:95. Answer: \boxed{76:95}.