When the checkbox is active, its square should be coloured and when is inactive it should be uncoloured.
To better illustrate this, consider the following current implementation:
Checkbox active: 
Checkbox inactive: 
Currently, IMO this behaviour is reversed and wrong, .i.e., they look to me like the checkbox icons should be reversed.
You can check that behaviour in overview -> Widgets -> Inactive.
Ideally, to avoid confusion, one would want a checkbox that displays sort of a cross when active, like this (with customizable color):
When the checkbox is active, its square should be coloured and when is inactive it should be uncoloured.
To better illustrate this, consider the following current implementation:
Checkbox active:
Checkbox inactive:
Currently, IMO this behaviour is reversed and wrong, .i.e., they look to me like the checkbox icons should be reversed.
You can check that behaviour in overview -> Widgets -> Inactive.
Ideally, to avoid confusion, one would want a checkbox that displays sort of a cross when active, like this (with customizable color):