In the beginning of the game "Sonic Adventure", what color Chaos Emerald does Tails own?

In the beginning of Sonic Adventure, Tails owns the purple Chaos Emerald. This is evident from the cutscene where Tails is seen holding a purple-colored Chaos Emerald while working on his airplane. The purple Chaos Emerald is Tails' emblematic color throughout the game, representing his character and abilities.