Contrary to popular belief, Chinese emperors and others in the imperial family would not have worn the more famous ceremonial Mianfu-robes during the Qin and much of Han Dynasty, but the more comparatively austere "Jūnxuán"(袀玄), which was a Qin invention, because they weren't into the Zhou-Etiquette informed Mianfu as Qin Kingdom then later Empire dedicated its state philosophy to Hanfeizi's Legalism.
(Which basically means Every Single Popular Depiction Of Qin Shihuang and Emperor Wu of Han you've likely seen are actually wrong hahaha)
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The robes (likely a one-piece shenyi, or upper and lower garments separated) were described as being "Xuán"(玄) or a reddish-black, because Qin Dynasty's national colour was black due to the idea of the Five Phases Colour theory, where each Dynasty had its corresponding Element therefore colour (Zhou Dynasty being Fire, & Qin being Water).
Other colours are reserved for the cuffs for the inner-robes for different seasons and occasions, with a white belt.
The headgear would have been a Tōngtiānguān (通天冠 AKA."Heaven-Linked Crown"), which was commonly worn by royalty (such as by Qin Shihuang himself(man being bowed to) on Sunjia Village's Han Dynasty pictorial brick-relief), or for the Western Han, a Chánɡɡuàn (长冠, AKA. "Long Crown"),
The Changguan was actually designed by Liu Bang himself, after his former headgear he wore when he was a local law enforcement officer, and was used by the imperial family-members of the Western Han Dynasty ever since.
Generally everyone in the court wore this robe during ceremonies, which means the only way you could have differentiated ranks between all the officials and with the emperor himself would've been their headgear, or more reliably the sash worn on the belt that worked basically like a service-ribbon of today
(The Emperor's colours were two shades of yellow and red, btw).
(Its quite similar to modern-day actually, with how all the politicians regardless of office just wear the same black two-piece suits all the time hahaha)
The Mianfu would see its return during the early Eastern Han Dynasty with Emperor Ming and stuck around ever since until the Manchurian Qing.
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Book of Later Han - Records on Clothing (后汉书 - 舆服志)
Tongdian - Rites, Chapter 21 (通典 - 礼二十一 - 君臣服章制度)
(Visual References in the attachments, if you want some!)