I get this too. They are slightly more regular and monochromatic geometric shapes than your example. I suspect the shapes may vary according to the loudness and suddenness of the noise, e.g. something big and heavy falling off a shelf in the room vs a car door slamming outside. I suspect I'd also see them in the day time if my eyes were closed, but there is so much other light and sound that the opportunity doesn't really arise. Like you say they are so fleeting that its hard to say the patterns move or change colour, but there might be a brief change as they flash in and fade.

Do the patterns move or change color?

No, it's a very bright, instantaneous flash; just a hanful of milliseconds, like a flashbulb going off. There wouldn't be time for movement.