As you will know from our discussion of why wetsuits are black, they are typically made from neoprene, neoprene is a material that has traditionally always been black.
The first days of synthetic rubber manufacturing produced an off-white milky color material. However, this rubber was unstable and did not have the longevity desired.
With this in mind, manufacturers began to add carbon to it. Carbon black is also known as soot and is dark black.
The carbon interacted with the polymers within synthetic rubber to create a new, more stable material. The result was a material called synthetic rubber also known as Neoprene. This was the name given to the material by manufacturer DuPont who invented it in 1930.
Neoprene was a far more resistant, tougher, and longer-lasting material than natural rubber. The black color helped to absorb heat and insulate, hence its suitability for wetsuits.