Lots of info!
The simplified version that I can grasp is that Low par and high alk can both produce faster growth.
Higher par produces color.
I think that having a bacteria driven tank [eating up and lowering nutrients], reducing Zooxanthellae [getting rid of brown protective coloring], causes an acropora coral to develop it's own pigments to protect it from the high par.
The trade off is that having colorful acros is at the expense of really fast growing brown corals. Once the brown colored Zooxanthellae have been reduced then the rate photosynthesis reduces also.
I think the ultimate goal, the holy grail of sps keeping is to have fast growth and incredible color. The people that achieve this have found the balance of reducing the Zooxanthellae, inducing pigmentation, all while pumping enough nutrients and bacteria through to keep the coral growing [ but not enough to cause a bloom in the brown Zooxanthellae].
This is about all that I am able to wrap my brain around.