Well.. the caste system was originally used to describe the Latin American system of racial hierarchy. The word "caste" comes from Portugese "castas". In reality similar systems exist elsewhere. Mauritania is an Arab Muslim country in North Africa, which has a racial caste system - Arabs/Berbers on top, mixed race (Arab/Berber mixed with Black Africans) in the middle and unmixed Black Africans on the bottom. Mauritania still has slavery; slavery of Black Africans.
The racial hierarchy in the Gulf is kinda complex. I lived there for a long time, a long time ago. Gulf Arabs are obvioulsly on top, then it is Whites from the rich powerfull Western nations then Levantine Arabs then North Africans then at the bottom are South and South East Asian, along with Africans, though when I lived there Africans were few and far between. Most Africans were Sudanese and Somalis. The menial labor / construction was totally composed of Afghans, Pakistanis, Indians, Sri Lankans, Bangladeshis, Nepalis. Filipinos were mostly housemaids, servers, service jobs. Lots of Sri Lankans and Ethiopians were also housemaids.
Gulf Arabs don't care if someone is Muslim, they give far far more respect , worth and importance to White Christians than to Muslim Asians. Race is a big factor but... a mixed race Gulf Arab (Black + Semitic Arab mix) is genrally a little higher in the pecking order than non Gulf Arabs (non citizens of Gulf countries) and non Arab Muslims, because at the end of the day he belongs to some Gulf Arab tribe. But he/she doesn't have the same worth as a 'White' Gulf Arab.
In Saudi there is a special detachment of Royal guards who protect the Royals; these guards are always from a specific African / Mixed African community. It's a heridatary job for them, so it's kinda like caste. But one of the most powerfull men in Saudi and the long time ambassador to the US , who was close with the Bush family, is Prince Bandar. He is mixed of Semitic Saudi (dad) and Ethiopian (mother). His mother is described as a concubine. In Arab culture lineage is from the father. So since his father was a Royal, he is treated as Saudi Arab royal and his mixed race isn't a factor.