Starfleet uniform (alternate reality 2250s)

The Starfleet uniform of the 2250s, along with many other changes in the timeline, experienced a slight change due to the temporal incursion by the renegade Romulan Nero. As a result of these changes, which included the premature death of George Kirk and the destruction of the USS Kelvin, Starfleet by the mid 2250s was using a different uniform in the alternate reality than the original uniforms which had been seen in the prime timeline.

As early as 2255, Starfleet was using the same "red/gold/blue" shirt design which in the prime reality was not introduced until at least 2266. The rank insignia had also changed slightly, consisting of silver bands on the sleeve, but with a thinner secondary band, rather than the previously used "hashmarks", for the ranks of lieutenant commander and captain.

The Starfleet insignia of the alternate reality was the delta/arrowhead design for all personnel, contrasted with unique insignia for each ship or base in the "prime" reality. The arrowhead design was originally the insignia of the USS Enterprise (NCC-1701) crew only and was not adopted as the insignia for all of Starfleet until around 2270. (Star Trek: The Original Series; ; )

Standard duty uniforms
The duty uniform consisted of a black undershirt, and a colored overshirt featuring the officer's division color and the Starfleet insignia. Rank stripes were displayed on the sleeves. Grey pants and boots were issued with the uniform. Female officers could wear either a uniform similar to the standard male uniform or alternatively short-skirted uniform not dissimilar from the prime universe equivalent - which itself had two variations, one with no sleeves and one with full sleeves. Without the sleeves however, these dresses did not display the rankings of each officer on them. 

Undershirt
Worn beneath the division colored shirt was a black undershirt bearing the Starfleet insignia, also in black. The undershirts also featured the arrowhead design present on the overshirt. It was acceptable for cadets and those unassigned to Starfleet to wear a Starfleet undershirt. 

Underwear
For use beneath their uniforms, Starfleet personnel had at their disposal specific undergarments. This underwear was a dark blue/green. 

Medical outfit
Some members of a shipboard medical staff wore a white overcoat, white trousers or dress. Violet scrubs were also avaliable for use. 

Engineering suit
A technician performing last-minute maintenance on Shuttle 89 was seen wearing blue coveralls. 

Environmental suit
The EV suit was used for operations within unstable atmospheres. The suit was available in all three division colors with a Starfleet insignia displayed prominently in the center of the chest piece and featured breathing equipment, including a helmet, for use outside of Class M environments. It could also be equipped with a parachute for orbital skydiving missions. A communicator was placed in the left glove. 

A copper armor-plated suit was used for inhospitable environments, such as the inside of a volcano. 

In 2259, a black-and-gold thruster suit was introduced for space dives. 

Field outfit
For cold environments like the planet Delta Vega, officers were given appropriate wear including a hooded jacket, gloves and boots. 

Wetsuits
Wetsuits came in two varieties: male crewmembers wore grey wetsuits with division colored piping, while female crewmembers wore designs with reversed colors (the primary color matching their division assignment; grey piping). The suits were also adorned with the same Starfleet insignia pattern as the regular duty uniforms. 

Flight suits
Introduced in 2259, these gray overalls were worn on shuttles. They had transparent yokes to show the division color, and the insignia was emblazoned on the upper arms. 

Dress uniforms
For formal gatherings, Starfleet personnel wore gray uniforms with high collars accompanied by a traditional peaked cap with the Starfleet emblem. Rank insignia was displayed by the standard stripes on the cuffs and by black lozenges on the shoulders, the number of shoulder device corresponded to the pip system that was seen used on the uniforms from the 2150s. Admirals wore uniforms with white jacket fronts. Ceremonial officers wore black uniforms with blue sashes. 

Starfleet Academy uniforms
Graduates of Starfleet Academy could wear the Starfleet Academy ring. 

Training uniform
While training on the Kobayashi Maru simulator at Starfleet Academy, cadets wore a simple blue-gray jumpsuit with the Starfleet insignia stenciled on the left chest, with no rank or class insignia. 

Junior officer dress uniform
Starfleet Academy cadets and junior officers (ranked Ensign, Lieutenant, and Lieutenant Commander) wore a red jumpsuit and jacket with a stand collar over a red turtleneck-like sweater; men wore pants while women wore skirts. On both male and female designs, the Starfleet insignia was displayed prominently on the collar of the jacket. On some occasions, cadets wore a red cap with the uniform. 

Senior officer dress uniform
Senior officers (ranked Commander and Captain) wore a black version of the junior officer's dress uniform; instructors at Starfleet Academy also wore this uniform. Barracks officers and shuttle officers wore a variation of this uniform which included a black cap. 

Flag officer uniform
Admirals and flag officers wore a cream-and-grey uniform for ceremonial purposes. Admiral wore one such uniform when transferring command of the Enterprise to. Starfleet Command Admirals such as Richard Barnett wore a silver tunic without any division colors while serving on the Starfleet Academy Board in 2258. Other flag officers wore this uniform with a cap of the same design, featuring the Federation emblem on the front. 

Section 31
Section 31 duty uniforms were a variant of the science division uniform with black sleeves. They also wore the black dress uniform. 

Rank insignia
The insignia used in the 2250s consisted of silver bands worn on the lower sleeve of the uniforms of line officers, or gold bands for flag officers. Enlisted personnel and officers holding the rank of ensign wore no rank insignia.

Rank on dress uniforms was indicated with epaulettes on their shoulders: ranging from one pin for ensigns, to five for admirals.

Background information
The uniforms seen in the films Star Trek and Star Trek Into Darkness were designed by Michael Kaplan. They are quite different from the pilot uniforms seen in and. It can be assumed that Nero's time tampering had something to do with the shift, although the real-life explanation is that the uniforms seen in Star Trek were intended to associate the audience with the much more familiar Original Series uniforms seen through the late 1960s, in contrast to the pilot uniforms, which were only seen in two episodes. A similar situation arose in where Leonard McCoy is shown in a flashback video wearing an Enterprise tunic whereas, historically, he should have been wearing an earlier pilot episode uniform. The filmmakers expressed surprise in Star Trek - The Art of the Film that the classic uniforms were never used in a film.

Kaplan explained that he selected red for the dress uniforms because of the strong patriotic feel the color gave. Admiral Pike's dress uniform was based on Admiral Kirk's dress tunic from. (Star Trek - The Art of the Film) In Into Darkness, Kaplan noted "There are a lot of high-powered meetings with Kirk and officers, and I wanted to add a level of sophistication, where – like any military service uniform – there would be different parts. So they now have dress uniforms, and shuttle suits, which they travel in."

For Spock's environmental suit, Kaplan used copper because he thought it was a beautiful color, but had never seen a copper spacesuit in a film. He did acknowledge that in reality, the metal would be ineffective against heat. The wetsuits were difficult, explained Kaplan, because "I wanted all custom colours, but we looked and they just didn't exist, so we ended up dyeing them, and through a lot of trial and error we found dyes that would work. Zoe Saldana looked pretty stunning in her red wetsuit, JJ's favourite costume. It was a big success putting her in a red wetsuit." Karl Urban said "We had a lot of laughs working in the wetsuits. They were very revealing."

The Starfleet ceremonial guard uniform appears to have been in post-production, as an on-set photograph shows the uniforms were brown with light purple sashes.

Apocrypha
Star Trek: Countdown to Darkness, Issue 2 depicts the uniforms of the 2230s had phased out by, at least, 2239 in the alternate reality, and replaced by this style. The only difference was that the command division was a slightly desaturated greenish-gold color. The comic book series also introduces a black excursion jacket to wear over the duty shirt, and a division colored apron.

In the Star Trek video game, Kirk and Spock don black-and-grey  to fly across a Gorn colony. The "wings" are green energy that are activated when skydiving.

Sternenflottenuniform (Neue Zeitlinie) 宇宙艦隊の制服（新時間軸2250年代）