Following applies for both the RHD and LHD model unless the car was re-sprayed.
Open the Driver side door.
Admire yourself of being the NSX owner.
Look at the door striker.
Depending on the country spec, you’ll find the sticker with the VIN/tire info/Safety Standard/etc.
You should see the Paint Code sticker nearby.
As a side note, you ‘may’ find Interior color code by opening the Passenger side door.
As a side note, even the OEM touch-up paint may no longer match the hue of your aged body paint.
Best asking body shop/professional to match your existing colour but matching the yellow is....
Kaz