If you arrive in JFK, say, from a "red" state you are expected to complete (or have completed) a special form and quarantine for 14 days. But if you started in a "green" state and only
connected through (< 24 hrs) a "red" from my reading of the rules you are exempt.
I arrived from LAS on Sept. 14 (at approx. 00:30), there were agents
at the gate handing out forms to complete--but Nevada went "green" that day.
On a more recent trip they moved the "form center" to the baggage collection area, with one agent for the entire terminal.
States are not separated by walls
, so crossing the street you can go between "green" and "red", making the draconian rules NYS has imposed just
seem like they are accomplishing their intended purpose.
Interesting case in point, Hoover Dam "bridges"* ARIZONA "green" on one side and NEVADA "red" So vacationing at HD, if you stayed on the NV side you must quar., but on the AZ side you don't.
*in the summer the clock on the NV side of HD is one hour different from the AZ side (no DST).