extract state changes from snapshot-based archive table

I have a table snapshot, storing snapshots (of the new state) every time an object stored in another live changed one of its attributes. I need to find all objects that changed a specific variable to a specific value in a given time frame.

For example, assume the following layout:

    CREATE TABLE snapshot
    (
        "timestamp" timestamp with time zone NOT NULL,
        person text NOT NULL,
        haircolor text NOT NULL,
        city text NOT NULL,
        CONSTRAINT snapshot_pkey PRIMARY KEY (person, "timestamp")
    )

Here, I want to find all persons that moved (from any other city) to NY between 2006-02-01 and 2006-02-14. I want all of them, even the ones that moved in on 2006-02-03 and moved out on 2006-02-05 again. (And of course I do not want to list people who only changed their haircolor in the given time frame).

What would an efficient query look like?