HERE'S an apparent contradiction that would be a classical case study for management students: How can a top brand be considered a black sheep by the stock markets? The sixth annual survey of India's top brands during 1996-97 conducted by A&M-ORG saw the fast-moving consumer goods giant, Colgate-Palmolive India, once again at the top, making up for its last year's defeat at the hands of Vicks. In five out of the last six years of the survey, Colgate has emerged at the head. Yet, the stockmarkets, considered the savviest barometer of a company's performance, don't seem to have a ring of confidence vis-a-vis Colgate's sparkle.