A branch of people believes that Jaati is a profession-based categorization of hindu masses whereas a Varna is a color based categorization of hindu masses.! People , the scholars, have even cited refernces from many Vedic documents to make their assertion and to prove them. But what sounds surprising to me is point that none of the scholars, particularly the English scholars, have attempted to understand the contextual sense of what the authors of those vedic documents have attempted to mean when they speak something about these two systems. For example, one cited Vedic document speaks that the four Varna/Jaati, whatever one may treat that for the time being, were created from the limbs of Manu-- the Brahmins being those from his head and mouth, the Kashtriya being his Arms and hand, the Vaishya being his torso and Sudra being his Legs...and for normal functioning of the society all have to do their duty, like for the case of human body.
Is it not surprising that scholar fail to mention the metaphor involved in the description above?? Does it anywhere mention that Brahmins were created from the head of Manu, to be taken as a serious note answer for "what is the origin of Brahmins ?" , or for that matter , " what is the origin of Kashtirya ?".
Similarly the word varna which duly has one of its meaning as Color, as in "woh shaym varna ke the " (he was of dark complexion). From this, a derivative comes that Varna was about color discrimination, and this further supported by another Vedic Document which mentions that Brahmins were fair complexioned, the Kastriya were Red, Vaishya were yellow , and Sudra weer black !
Being a hindu, I have hardly felt the existence of color discrimination in our people, although a preference for a "gori bahu" (a fair complexioned bride) is seen. But even then, the above remains only a simili/metaphor in my opinion, while the vedic author of the above might have been attempting to theorise how the Varna difference might be showing up, (as in, a V-shape underwear may mean that the wearer is likely to be a sporty chap, or 'Lord Lochinvar' means he was a noble person, although he was a 'the highway man'), which the English Scholars of Indians Sociology have almost successfully managed to thrust in the minds of our, hindu youngsters, to the extent that color discrimination might begin now, even when nobody is red or yellow. While a 'dark Brahmin' may be actually falling out with his distractors about his Brahmin status, or otherway, the standards of 'Fair complexion' as assigned to the Brahmin club.!!
That will be the tragic irony of myths created by English Scholars while studying Indian System, which is prone to accepting the outside observer as a Judge impartial !!
The word Jaati I think remains that of the Vedic origion, but has to treated as something connoting a tribe. There are other usages, such as jan-jaati, janya, to mean the 'club of people' but , as i see them, referentially to mean the Tribe of people who share a common descent. It is in this regard that there are Vedic mentions of 'Panchjanya' to mean the five tribes of early vedic people. A janjaati is impling- 'those people who are commonly found in a given territorial area', a small town, of a forest region, etc. Thus a Jaati, spoken of as Caste in English ('casto' a portugese origin for the word caste), is suppose to mean a birth/hereditrical/genetic categorisation of people. A Varna on the other hand is likely to mean a work/profession based categorisation. The word, Varna, has an alternate meaning as "categorisation/ distinction/ or description' itself,(a close derivative of Varga; Varnamala meant the alphabets in Sanskrit; the word "Varanan' means the act of describing something. ), apart from the previous meaning 'Color'.
Thus a person from any Jaati was accepted to come to any Varna depending upon how he fared-- behaved/conducted/practised his vocation.
The examples of Jaati would be-- Saini, Kurmi, yadav, raghuvansh, jaat, Puru, khatri, etc.
But for the Varna-- there are only four of them-- Brahmin, Kshtriya, Vaishya, Shudra.
It is here that one can note there is no Jaati as Brahmin. In fact, all the four Varna are Status only, which people from any of the several Jaati attain by virtue of their accomplishment. But the modern Indian scholars, and also the common people, interpret it as one and same, which for some natural psychological causes is not too far from reality for the reason that Children do acquire the traits if the parents better than anyone else, and hence become almost one and the same. The further affirming of uch mistaken belief of seeing them as one is attibutable to the treatment and recognisation to the system in this manner by the past Invading rulers of India, the Moghuls and the British.
Another cause of confusion of Jaati and Varna to come around in Indian society was the fact that the descendants of the Varna- Brahmin, the people who attained a high state of wisdom, the Brahmmah , and thus provided discretion on Good and Evil, and also gave Prudence thoughts to the people at large from rest of the Varna, the descedants attempted to retain their high social status, by releasing it from the clutches of continuous attainment of wisdom, the Brahmmah, by putting Brahmin also as a Jaati. This was one of the first cases of moral corruption by high wisdom people. One can very plainly note that among all Jaati and Varna as known to Indian system today, only the Brahmin are both (!!) a Jaati and also a Varna. The causes of this can be plainly understood, and more when one tries to explore the origin of Brahmin as Jaati in the Vedic Literature.