You'll want to add an instance variable to the nodes and when they are created pass something like the UID/IID of the blue square to the nodes, then have the pick condition include node.variable=bluesquare.UID/IID
EDIT: I couldn't understand your events so I have created an alternate event sheet with different variable names and switched to move to behaviour to demonstrate.
1drv.ms/u/s!AkmrWgxeuxlKhIcV4LyHc4pXO6CSVg