The following text contains spoilers about:
Mass Effect 1 - Tali and the Geth (Tali's personal quest)
Mass Effect 2 - Tali: Treason (Tali's loyalty mission)
Mass Effect 3 - Tali's general development and role in that game
I’m pleased that the imminent destruction of all organic life has improved your career opportunities.
~Tali'Zorah nar Rayya
That's what Tali said to Garrus on an elevator ride in 2183. The same circumstances boosted her performance on her pilgrimage and several years later even her career.
In Mass Effect 1 Tali can get the opportunity for gathering valuable Geth data from a Geth stronghold on Solcrum providing something of great value for returning to the Quarian Migrant Fleet which is the main purpose for any Quarian's pilgrimage. In 2185 Tali gets assigned with a research mission by the Admiralty Board. During this time she secretly sends Geth artifacts and components she considered save and harmless to her father Admiral Rael'Zorah for conducting research on how to gain an advantage in the long-lasting Quarian-Geth-conflict. Tali later recovers that data which leads to a partial understanding for her on why her father was conducting such dangerous research. Du to her fathers passing and her expertise of the Geth Tali gets promoted to Admiral in 2186.
Unfortunately we don't get to learn what the Quarians learned from the data Tali recovered and from the experiments her father conducted. My ideas for this outfit of Tali started right there.
The way Bioware designed Tali's enviro-suits was always great. Her standard appearance in Mass Effect 2 is beautiful. Originally I didn't want to design an alternate appearance for Tali because of that. There was no real need. On the other hand I didn't feel like leaving her out of my list of alternate appearances. Using Tali's background I started working on several drafts involving the Geth data available due to her and her father. First I took a closer look at the Geth. Their basic anatomical shape has some striking resemblance with the Quarian anatomy. Considering that Geth were created by Quarians as "servants of the people" it makes sense that they share certain anatomical traits. That came in handy when creating something new for Tali.
If Tali spent enough time with Legion she considers the possibility of peace between Quarians and Geth. Following all of that Tali used save-to-use Geth components she obtained and created a sturdy and protective new enviro-suit for her in the ongoing war against the Reapers. Some parts are taken and remodeled from her alternate enviro-suit of Mass Effect 3. Due to limitations of resources Tali couldn't fashion a whole new suit entirely based on Geth components. The chest-plate consists of reshaped components from the chest of Geth rocket trooper while the armor on the back shares features of Geth components and Tali's enviro-suit of Mass Effect 2. The same goes for the armor on her upper thighs while her lower thighs are protected with parts from a Geth Armature while wearing parts of her original enviro-suit underneath her new armor. Her arms are covered by a very light soft material for allowing flexibility. At first I wanted to use parts of a Geth Jumper for that but that wouldn't have looked right. The enviro-suit is covered by gloves made of the iconic fabric Tali has been wearing since the first time we met her in the Wards of the Citadel.
Matching her rank as an admiral of the Migrant Fleet something that would be described as an epaulette best is attached to her shoulder. Epaulettes are used for displaying a military rank in real life. They are usually added to both shoulders of the wearer. Following that I wanted something similar for Tali yet different enough for not just being a copy of what we have in real life. My first thought was that it has to be asymmetrical so I reduced it to a single epaulette. This Quarian epaulette consists of a metal plate installed onto the enviro-suit. Instead of the usual fringes hanging off the shoulders I replaced them with Tali's iconic fabric with a cut in its middle so that it falls nicely. That way it resembles her rank as an admiral but it can also be used as an identifier.
Since Quarians can't just change clothes I wanted something that would make this a bit more combative attire look suitable for her duties as an admiral. So I fashioned her some sort of skirt. Something that can be put on and off easily without having to remove the enviro-suit for that or getting it in the way. The importance of her traditional fabric became clear once more. Since we can't see Tali's face her most distinguishable feature is her violet fabric with its delicate pattern.
That way her appearance can be divided in two major elements. The armor part which consists mostly of black and white/grey elements and the parts covered by her violet fabric making it her personal enviro-suit.