Dark blue, also known as navy blue, is a deep, rich shade of blue that is versatile and elegant. When describing the color, there are a variety of synonyms that can be used to convey the same meaning or create a slightly different hue. Some alternative descriptors for dark blue include sapphire, indigo, cobalt, midnight, royal, navy, and deep blue. Each of these words carries its own connotations and associations that may be useful in writing or conversation. Ultimately, the choice of synonym will depend on the specific context in which it is being used and the desired effect on the listener or reader.