Compare instance variables for 2 instances of same object

What's the simplest way to compare instance variables for 2 or more instances of the same object?

In the CAPX below, I want to destroy overlapping blocks only when they are of the same color but at the moment all overlapping blocks are destroyed regardless of color. I have seen some forum posts mention using local variables but I could use a simple example to illustrate this.

sendspace.com/file/ur8wzd

you need to use families to test between same objects

So I would put the block sprite into 2 different families and test for overlap between families? Would I then need to create family instance variables and compare these? Appreciate if you could modify my CAPX to illustrate.

put the object in a family and in the event check the object and the family, with family behaviors

https://db.tt/ViQsQ1RW