Why are presidential cars always painted black?

Excerpt
For centuries, monochrome black was the customary color used or applied to many works done: drawing pictograms, writing manuscripts, and even in painting carriages and coaches. Its application was due to practicality or expediency.
A general sample is the ‘black’ thick India ink, which was used by many artists and calligraphers throughout the centuries. Emitting a certain odor, its popularity only diminished with the introduction of better odorless inks and paints today.