I will opine that a significant and major reason it looks so much greyer is the function of the raised grove's decking surrounding the base of the trees - previously, those existing mature trees were surrounded by grass / greenery at their bases. Unfortunately, apparently heavy usage compacted the soils around the roots enough that it was threatening the tree's health, so the solution was the raised grove's decking.
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That allows the soil & therefore root systems to be healthier and keep the trees alive, but because it's now a elevated concrete plank deck instead of natural dirt & grass it is visually grey, even if the soil underneath is happier. Perhaps the city could have chosen a more natural color palette (which yes was inspired from BPL) but it'll probably age well. I'm still going to reserve judgment until the full thing grows in - those young trees will need time.