How are black green and oolong different tea?

Oolong tea gets partial fermentation, and often an additional shaking/bruising step that release additional flavors. Oolong can range in color from dark green to black. The combination of bruising and partial fermentation give many oolongs distinct flowery & earthy flavors. Darker oolongs may have buttery or smoky tastes to them. It has somewhat more caffeine and less antioxidants than green tea.

Black tea is fully fermented, which blackens the leaves and causes the formation of caffeine and tannins. It generally possesses the most robust flavor and highest level of caffeine, but the least antioxidants.

Green tea has a minimal amount of oxidation, halted by additional pan-frying (Chinese teas) or steaming (Japanese) steps. The additional processing brings out more flavor, and allows for caffeine to develop, at the cost of a reduction in antioxidants. Characteristic flavors are grassy, vegetal, and earthy, with sweet notes.