You are doing great!! I actually like the roof height.. I wasn't able to figure out the roof with the little window piece. Totally spacing what those are called at the moment, so I went with what I did.
The reason the pillars are a different color of white (I'm thinking) is because of the material they're made out of. For example, different wall coverings could be the same color, but depending on what type of wall cover you use it could look a different shade.