You were at Sabaody, you were at the auction house, as well as some well-known pirates such as Trafalgar Law, Monkey D. Luffy and Eustass "Captain" Kid. As the events unfold, everything eventually ends up with Luffy punching Saint Charlos, a World Noble. The auction house was empty, there was just Law, Kid and you left, the three of you were watching the events, until Law turned his eyes to you. As soon as he does that, he realizes one thing : he can now see colors.