Hello! The garments of a concubine/consort of high-ranking men varied according to two factors: the time period and if they were civil or military aristocrats.
In Heian period (794-1185), the civil aristocracy (kuge) from the Imperial court retained political power - therefore, they were the high-ranking class. Court ladies (including wives, consorts and daughters of court officials and noblemen) wore junihitoe, ("12 layered robes", althoug the actual number of layers reached 20 in some periods). You can read/see more about junihitoe here, in this chart from my DeviantArt gallery.
A modern replica of Heian period junihitoe.
From the end of the Heian era, the military aristocracy (buke/samurai) gained more and more status, and the political power shifted towards figures like the shogun and provincial lords (daimyo), from the buke class. Samurai ladies wore simpler garments than civil/kuge ladies. During the Kamakura-Muromachi-Sengoku eras that followed, they wore kosode combined with thin obi and a few layers of outer robes (uchiki) over it - no more hakama or mo. Kosode was the "grandpa" of modern kimono, wider and with short sleeves, sewn to the main body - like in modern men's kimono.
This style with kosode+thin obi+uchiki was worn by high-ranking samurai ladies (including wives, consorts and
daughters of the shogun and daimyo) during about Momoyama to Sengoku periods. The hair, as in Heian era, was worn
long, loose or tied at back in suihatsu taregami style. Photo from Jidaya Arashiyama.
During the Edo period (1603-1868), the kosode slowly became less wide and the brocade/dying techniques advanced, transforming towards the kimono we know today. There was a lot of variation in fashion during the centuries. But, for an example of this period... At the XVIII century, wives and consorts of shogun/taiko/daimyo used to wear koshimakitsugata, i.e., "koshimaki style"- an over-robe tied at waist. Althou high-rank samurai ladies used to tie their uchiki at waist during summer since the Muromachi era, at the height of the Edo period this "evolved" into a specially flamboyant style, with a special obi to keep the uchiki's sleeves open while the koshimaki was worn.
From left to right: Sengoku period koshimaki style, worn on summer, and Edo period-style koshimaki. In Edo period, the special obi (koshimaki-obi) kept the sleeves open, creating a "wide wings" effect on the waist. Photos from the Kyoto Costume Museum.
As typical from the Edo era (specially in its later period) straight low-tied hairstyles often changed into complex buns. Several styles existed, and were worn by specific class of women. Some hairstyles were for commoners, other for rich merchants, other for geisha, other for noblewomen, etc... This is not my specialty field, so I won't say much about it... ^^; But you can check out some examples of nihongami (traditional japanese hairstyles) and their use in this deviantart gallery.
A TV drama's costume of a lady from the Ooku - a term that despicted an isolated area of the castle were
lived all women related to the shogun (or powerful daimyo), such as their mother, wife, consorts/
concubines and daughters. This costume is related to the Edo period.
Meanwhile, civil court ladies from the Imperial palace still wore very traditional junihitoe for formal occasions, even during much later periods than Heian. Junihitoe worn by Imperial family ladies in XIX century had little differences compared to Heian period ones. The most visible change was the hairstyle, called osuberakashi, that had a high "lamp-shape", and was worn with golden hair ornaments.
Heian era junihitoe (left) and end of Edo era junihitoe (right). The most significant change in Imperial
ladies' formal garment during these distant periods was their hairstyle.
A close-up on Edo period osuberakashi hairstyle.
...I hope this helped at least a bit on answering your question, Orangenbluete! Sorry it's just a quick overview, but this is a quite wide topic (which I'm not an expert at, I must admit! ^^;). Any other questions or if you're interested in more about a specific time period for consort-concubine garments, feel free to ask!