You have to continue reading but what they refer to as putting the "hair" bulb in a chemical solution (DOPA) is proving or disproving the presence of Tyrosinase. If no Tyrosinase is present, even though the chemical solution provides the necessary DOPA for the production of melanin......no melanin will be formed indicatimg a T negative form of albinism. It basically is proving the absence of tyrosinase in the test subject by artificially providing the neccessary Dopa. If tyrosinase is present but unable to mix in the test subject, when put with the chemical solution (DOPA).......melanin will form indicating a T positive form of albinism.

Here is the section this came from:

How do we classify Oculocutaneous Albinism?
The classification of OCA has changed a great deal over the years, with much of the work coming from the International Albinism Center and the help of all of the wonderful individuals and families who have helped with these studies. For many years, the term "albinism" referred only to people who had white hair, white skin, and blue eyes. Individuals who had OCA and pigmented hair and eyes were identified, particularly in the African and African-American population, and terms such as 'incomplete albinism', 'partial albinism' or 'imperfect albinism' were used for this, but these terms are inappropriate and are no longer used. In the 1960's, Dr. Carl Witkop developed the hairbulb incubation test to separate pigmenting and non-pigmenting types of OCA and started to use the terms "ty-neg" or "tyrosinase-negative" and "ty-pos" or "tyrosinase-positive" OCA. Freshly plucked hairbulbs from a person with OCA were placed in a solution of tyrosine or dopa (see Pathway above) in a test tube and watched to see if pigment formed in the pigment cells in the hairbulb. If no pigment formed, the test was negative and the diagnosis was ty-neg OCA. If pigment formed in the hairbulb, the test was positive and the diagnosis was ty-pos OCA. Although this simple test showed that there were different types of OCA, subsequent studies have shown that the hairbulb incubation test is not very sensitive and has many false negative and false positive responses. As a result, the hairbulb incubation test is no longer used in the evaluation of an individual with OCA.

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Tom Burke
www.BurkeReptiles.com

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