Impossible to pass object as argument to a function

When trying to pass an object (the id of an item) as an argument to a function, one gets the following error: "TypeError: incompatible type of argument(s) in call to changeCol(); candidates were changeCol(QVariant)", see attached file. When clicking in the window, the blue rectangle should become red.

If the function is defined within a "Script"-block, it works as it should.