The Gelug or Gelukpas are the Yellow Hat sect of Tibetan Buddhism: The Red Hat sects are Nyingma, Kaygu and Sakya

 begin quote from AI and Internet:

 

The Red Hat sects collectively refer to three of the four major schools of Tibetan Buddhism—Nyingma, Kagyu, and Sakya—which are named for the red hats traditionally worn by their monks during ceremonies, in contrast to the "Yellow Hat" Gelug School. The Nyingma school is the oldest and was founded by Padmasambhava. While Nyingma is sometimes considered the sole "Red Hat" sect, the term more broadly encompasses Sakya and Kagyu as well. 

Key Characteristics:

• Color of Hats:

  The term "Red Hat" comes from the color of the monks' hats, worn during formal occasions. 

  
  

Schools Included:

• Nyingma: The oldest tradition of Tibetan Buddhism. 

Kagyu: Also known as the Oral Tradition. 

Sakya: Known for its "Grey Earth" tradition. 

Distinction from Yellow Hat School:

In this classification system, the Nyingma, Kagyu, and Sakya schools are grouped under the "Red Hat" designation, while the Gelug school is known as the "Yellow Hat" tradition. 

Focus:

These schools emphasize tantric practices, such as the Dzogchen (Great Perfection) doctrine, particularly within the Nyingma tradition.