Local laws apply to all. Nepalese seem have few more privileges.
Have not traveled recently. We have seen many best and worst stories in Sajha. Things seem to change a lot every now and then. Customs does not know up front whether you have US or Nepali passport. I believe they don't try to give hassle to US passport holders. Also, there has been some major media turmoil about airport irregularities recently. Hopefully they will not be too unreasonable.
No experience with Red channel. Always went green.
1. Fly with Singapore and Cathay - there were numerous customs staff asking and questioning (assuming they normally get affluent passengers)
2.Went to Nepal with Emirates before we learned that it is the worst airline (FlyDubai). None of the passengers was stopped by customs (all passengers are low wage laborers from middle-east)
3. Fly via India. Customs doesn't even look at your 'nepali looking' face
Have a great trip!