The colour blue is expensive, and always has been. Although modern production has almost completely leveled the price of different colours, blue is still difficult to find in natural pigments and, therefore, very expensive before the onset of industrial chemistry.
Egyptian blue is the oldest synthetic pigment known to man, and at the time of its creation, in ancient Egypt, it was also the most expensive in the world. Ultramarine was obtained from semi-precious stones imported from the East (hence the name), so, logically, the pigment extraction wasn’t very affordable either. Prussian Blue is named after the colour used to dye the uniforms of the Prussian army: can you imagine why this shade was the perfect option for such a strong army? Any advertising exec can now tell you why!