I wouldnt worry if the color is shifting, I would worry if its bleaching and/or receding off the skeleton. The OME can change quite a bit, I beleive the one at WWC is a similar color to the one you mentioned and thats most likely due do lighting intensity one way or another. You can check if your alk swings by testing it once then test it again in 24hrs and see if theres a large difference. Its really important to dose regularly to keep everything stable, your pH sounds fine which means you probably do. One more thing to keep in mind is temperature swings, if thats in check too then I would raise mag and cross your fingers lol, also try feeding them at night if you dont already.
