Is caste system a product of colonial rulers?

Rightest wing intellectuals are getting strong hold in the main national stream of intelligentsia and they say that there is no caste system in India, but there are castes here, but no caste system. They state that this caste system which is not in existence is the creation of colonialism. But my contention is that there was caste system even before colonialism has entered in our country. Many instances in the previous scriptures like the Ramayana and the Mahabharata we can quote the system prevailing in our ancient past. Bhagavan Buddha in his Chula Vagga refers to caste system that prevailed in ancient India. Can anybody throw light on this?