why does it have a multi-colored stripe in the middle?

It is part of the foundation for the second floor.
I repainted the exterior walls to make them blue only, rather than blue and light blue. I was a little worried this might make it look a little dull, but it seems to make little difference.

I dont see why people make blue houses... I've barely seen any blue houses in my life
inb4 someone tries to prove me wrong with a random blue house.
Painting the exterior beige would look sort of dull. The interior walls are beige.