I can't think of any reason why they would have added brown pigment for that concrete, so perhaps it get poured with the leftover concrete from someone else's pour - someone that was using brown concrete.
They have started the big pour (although any pour seems small compared to The Bow pour now!) tonight, 3 pumper trucks set up and 2 running as I type this. Pics are mine:
Update for August 6th, they have poured the first part of the parkade floor in the southwest corner. Continuing to dig out the area near the second crane base for the foundation of the third tower.