Complex sentence: In the early 1950s and 1960s, when many of the city's inhabitants were poor, the small houses were all painted white and blue--colors that represented the sea and sky and were considered the city's official colors.
Split into simpler sentences: In the early 1950s and 1960s, when many of the city's inhabitants were poor, the small houses were all painted white and blue. These colors, representing the sea and sky, were considered the city's official colors.