So are you saying there isn't supposed to be a visible Leaky Cauldron entrance at all and that the change in brick color is just some random mistake?
Seriously, this whole "Universal guests are Muggles, not wizards" think is a bit of a pain in the arse. We'll have access to Diagon Alley, Hogsmeade, and Hogwarts, we'll have working magic wands, we can purchase house robes and wizarding supplies, we can see 12 Grimmauld Place (can't we?), but we're Muggles. Everything requires some sort of convoluted story just to make sense of it. Wouldn't it just be easier to treat guests as witches and wizards? "Oh look - it's the entrance to Leaky Cauldron or Hogsmeade or the Ministry of Magic (plan 3), and you know that because you're a witch/wizard!" Makes so much more sense.