I would like to help, but I am not sure what you are looking for.

Edit:
Just found out that a cube has different outputs like OnFizzled, OnPlayerPickup but I didn't found anything like 'being hit by laser' or something. Maybe Skotty can find a solution for your problem...

I don't think there's a way to do that directly, but you can fake it.
Place a small trigger in the center of the button.
Create a filter_activator_class with the class name set to prop_weighted_cube and the filter mode at Allow. Name this.
Go back to the trigger you created and set the filter name to whatever you named the filter_activator_class.

Create an output on the trigger with the output name OnStartTouch. Then, put in whatever you want to happen when the cube changes skins.

Courier6 wrote:
As in when the cube's skin changes from light blue (or pink) to yellow?

I don't think there's a way to do that directly, but you can fake it.
Place a small trigger in the center of the button.
Create a filter_activator_class with the class name set to prop_weighted_cube and the filter mode at Allow. Name this.
Go back to the trigger you created and set the filter name to whatever you named the filter_activator_class.

Create an output on the trigger with the output name OnStartTouch. Then, put in whatever you want to happen when the cube changes skins.

This plus a math_counter so it actually has to be activating the button