/u/Vepr157 has two great photo essays: An album of American nuclear submarine propulsors (screws and pumpjets) in roughly chronological order and Everything You Ever Wanted to Know about American Second Generation SSNs (Permit, Sturgeon and Narwhal) that cover the evolution of US submarines.

In the US, the teardrop hull was first pioneered in the experimental diesel-electric boat USS Albacore. The Albacore was part of a larger trend within the USN submarine community to try and incorporate the lessons of WWII and make submarines much more effective underwater. The teardrop lessened hydrodynamic resistance and allowed submarines to travel at unparalleled high speeds underwater.

The typical WWI and WWII submarines were not true submarines, but rather submersible ships. These subs were to spend most of their patrol chugging along on the surface of the water their diesel engines and submerge when they approached an enemy force under battery power. This need to spend time on the surface was why these submarines resembled surface craft. The problem was that submarines were extremely vulnerable on the surface with the advent of radar and the growing ubiquity of aircraft. The Germans u-boat arm pioneered a number of innovations such as the Schnorkel which allowed for U-boats to use their diesels underwater and purpose-built designs like the Type XIII and Type XXI which were meant to spend a good deal of their time underwater. These German developments proved highly influential for the Allied submarine development postwar. Both the Soviet diesel-electric Whiskey-class and nuclear-powered November-class used the Type XXI-inspired hull form.

In the US, the aptly-named Greater Underwater Propulsion Power Program/GUPPY retrofitted American WWII submarines with more streamlined sails and made them overall more suitable to cruising underwater for longer periods than when initially launched.

The GUPPY program influenced the Nautilus design, but it was the greater success of the Albacore's teardrop hull that showed the way forward. Both the diesel-electric Barbel-class and the nuclear-powered Skipjack-class used the teardrop hull. The advent of Hyman Rickover meant that nuclear propulsion would be the way forwards for the USN, and this meant that the teardrop hull would remain the dominant hull form for US boats. Nuclear power meant that the ships did not need to cruise on the surface at all.

Ironically, despite being an advocate of nuclear technology, Rickover's instincts towards other aspects of submarine design were actually quite conservative. American sail designs remained roughly the same shape since the Skipjack, even though advances in metallurgy and testing could have led to a quieter and more efficient sail. Rickover scuttled the CONFORM project which would have produced a sailless, streamlined sub optimized for high-speed in favor of his more conventional 688-class design. Contrary to Tom Clancy's fiction, it was the Soviet navy that proved more innovative and open to new design elements. Both in hull form and in materials used, the Soviet design bureaus tasked with producing submarine designs were more willing to take risks and push the envelope of what was possible. Experimental boats like the Papa-class proved the feasibility of greater streamlining and Soviet submarines tended to have more squatter sails both underwater performance and to reduce noise. The cumulative result of these experiments in the 1960s and 70s was that the Soviets began fielding submarines that quickly closed the operational capabilities gap between American and Soviet submarines. In his book Cold War Submarines, Norman Polmar relates an amusing anecdote from one of the Soviet Malachite bureau designers:

We had competition in submarine design. You [in Rickover] had Stalinism!

Edit: There was also another factor aside from hydrodynamics that encouraged the teardrop hull form: sonar. One of the challenges for naval designers in the Cold War period was to find space for the sonar arrays as they became larger. This installation of a soar array on a Permit-class gives a good indication of its size- and this album has a bunch more pictures. The bow was the best spot for this sonar as it allowed for an unobstructed forward view and some degree of side view. As these spherical arrays got bigger it made sense to house them in a streamlined bow housing; uneven water turbulence could degrade sonar performance and the drag from a dome could cut into speed. The teardrop or some variation of this hull form was a way to get around this problem. The fiberglass or other materials used to cover the sonar domes sometimes created a differential appearance on the boats' markings as these materials reacted differently to the antifouling paints.

This is a segue to the question of why submarines are often black or dark grey. The standard rationale for this is that this would lessen the visual signature of the sub when it was operating at periscope depth (ca. 50-70 feet-although firm numbers are hard to come by because navies do not like to publicize exact performance numbers). The black color makes the submarine look like a shadow or blend in with the murk of the water.

However, black is not always the best color for camouflage and it can be conspicuous in the right circumstances. During the Cold War when many subs expected to fight it out in the Atlantic or Barents Sea, black made a certain amount of sense. But as submarine missions have shifted in the post-Cold War world into littoral zones or the clearer waters of the Pacific or Indian Ocean, some naval personnel are rethinking black. HMS Torbay recently used a nice shade of blue and Iran's indigenous-Fateh submarines use a shade of green while others have a turquoise suitable for coastal operations. Kim Jong-Un recently toured in the DPRK's antiquated Romeo-class in a nice green shade. But these color variations are the exception rather than the rule and basic black appears to be the dominant color for submarines as it was in the Cold War.