The assignment: Use at least 4 different hues (colors) of blue in a composition that includes architecture. Architecture is defined as anything manmade.
Purpose assignment: To learn more about blue hues including value (light and dark) and chroma (intensity or strength of color).
Consider: Making a color Chart of each hue (color) before making your painting. Begin with the strongest chroma of blue, then add white, black and gray to vary the value and chroma.