All the doors to the blue building are locked with the blue field but inside is a red door. How do you get the red stone inside to unlock this door?
If you look around the back of the blue building when it is small, you will see there is a sort of ramp going down toward a blue field. Look even closer and you will see a small red crystal at the top of this ramp. Put the round red stone here and it will roll down and stop at the blue door. Go inside the blue building and when you unlock the second door I side, the red crystal will roll down and I side the building where you can pick it up to unlock the red door inside.