After a few inquiries I thought I should explain.
The rooms in these houses flow in a straight line one into the other. It was said that if you fired a shotgun at the front door the bullet would exit the back door, thus the name "shotgun house."
The yellow one is a single shotgun and the one next to it is a double shotgun with two doors and two rows of rooms.
The shotgun houses of New Orleans can be very plain with just shutters and shutter doors or they can have gingerbread trim on them. They are unique in their coloring and it is considered an art to combine many colors in paint and trim. Most of the shotgun houses of New Orleans are built of cypress.