The author of the blog post What's your Varna quotient? uses a certain definition of varṇa:
The generic definition of the term 'Varna' comes from 'Vriyate Iti Varnaha' implying that one can choose the group and occupation based on your innate tendencies. "Just as a wooden toy elephant cannot be real elephant, and a stuffed deer cannot be a real deer, so, without studying scriptures and the Vedas and the development of intellect, a Braahmana by birth cannot be considered a Braahmana" says the Manu Smriti [2.157]. A hymn from the Rig Veda goes to the extent of saying, "No one is superior, none inferior. All are brothers marching forward to prosperity."
What is the source of this explanation/etymology? Is it taken from Hindu scripture or one of the Sanskrit dictionaries?