how separate overlapping objects?

Hello, I have an image with two overlapping squared objects of the same size and colour. They are on a uniform backround and one object exceeds the other from the left with with a 10 degrees tilt. I need to extract the object on the top. How can I proceed?. Thanking you in advance for your help.

[Rob]

sorry, I said same colour but in fact they have different shades of blue but small variation.