《内经》曰∶脉以应月，色以应日。色者，视之易见者也。如伤风阙庭必光泽。伤寒，
阙庭必暗晦。面青黑为寒，为直中阴证。紫赤为热，为传经里证。若已发汗后，面赤色盛，
此表邪出不彻也，当重表之。又阴盛隔阳，合面赤色，是为戴阳之候，宜急温之，以通阳气
大抵黑色见者多凶，为病最重，黄色见者多吉，病虽重可治。经云∶面黄目青，面黄目赤
面黄目白，面黄目黑者皆吉。盖黄属土，今恶症虽见，土犹未绝，故可救。若面青目赤，
面赤目白，面青目黑，面黑目白，面赤目青，皆难治也，言无土色则胃气已绝。凡天庭、印堂、
年寿等处，黑色枯槁者凶，黄色明润者吉。然人有五色，不能齐等。经云∶五色者，气之
华也，赤欲如白裹朱，不欲如赭。白欲如鹅羽，不欲如盐。青欲如苍璧之泽，不欲如蓝。黄
欲如罗裹雄黄，不欲如黄土。黑欲如重漆色，不欲如地苍。五色之欲者，皆取其润泽，五色
之不欲者，皆恶其枯槁也。经又云∶五色精微象见矣，其寿不久也。言五色固不宜枯槁，若
五色之精华尽发越于外，而中无所蓄，亦非宜也。大抵五色之中，须以明润为主，而明润之
中，须有蕴蓄，若一概发华于外，亦凶兆也。察色之妙，不是过矣。
经曰∶五色决于明堂。明堂者，鼻也。故鼻头色青者，腹中痛。微黑者，有痰饮。黄色
者，为湿热。白色者，为气虚。赤色者，为肺热。明亮者，为无病也。若伤寒鼻孔干燥者，
乃邪热在阳明肌肉之中，久之必将衄血也。病患欲嚏而不能者，寒也。鼻塞浊涕者，风热也
鼻息鼾睡者，风温也。鼻孔干燥，黑如烟煤者，阳毒热深也。鼻孔出冷气，滑而黑者，阴
毒冷极也。凡病中鼻黑如煤，乃大凶之兆。若见鼻孔煽张，为肺气将绝之证也。凡产妇鼻起
黑气，或鼻衄者，为胃败肺绝之危候，古方用二味参苏饮加附子以救之，多有得生者。
《黄帝内经》说：脉象的变化对应月亮的盈亏，面色的变化对应太阳的明暗。面色是肉眼容易观察到的。比如伤风（外感风邪）时，阙庭（眉心及鼻梁上部）必然光泽明亮；伤寒（外感寒邪）时，阙庭必然暗淡晦涩。面部呈现青色或黑色，属于寒证，或者是寒邪直中阴经的证候；呈现紫色或赤色，属于热证，或者是病邪传入经络内部的证候。如果已经发汗后，面色依然红赤显著，这是表邪没有透发干净的表现，应当再次使用解表法。另外，如果是阴寒内盛格拒阳气，导致满面通红，这是“戴阳”（虚阳上浮）的征候，应当紧急温补，以通达阳气。大抵来说，出现黑色多主凶险，病情最重；出现黄色多主吉祥，即使病情严重也可治愈。经文说：面色黄而目青、面黄目赤、面黄目白、面黄目黑的，都属于吉兆。因为黄色属土，现在虽然出现了恶症，但代表脾胃之气的土色尚未断绝，所以可以救治。如果面色青而目赤、面赤目白、面青目黑、面黑目白、面赤目青，都难以治疗，这是因为没有黄色的土色，说明胃气已经断绝。凡是天庭（额头）、印堂（两眉之间）、年寿（鼻根至鼻尖）等处，如果出现枯槁的黑色，主凶；如果出现明润的黄色，主吉。然而人的五色不可能完全均等。经文说：五色是脏腑精气的外在表现，红色应该像白绢包裹着朱砂那样含蓄润泽，不应该像赭石那样枯暗无光；白色应该像鹅毛那样洁白细腻，不应该像盐粒那样干枯刺眼；青色应该像青玉那样温润有光泽，不应该像蓝草染料那样死板；黄色应该像丝绸包裹着雄黄那样柔和明亮，不应该像黄土那样干燥浑浊；黑色应该像多层漆色那样深沉光亮，不应该像地苍（一种矿物）那样灰暗。五色所“欲”（喜好/正常），都是取其润泽之意；五色所“不欲”（厌恶/异常），都是厌恶其枯槁之态。经文又说：如果五色的精微之象显露无遗，病人的寿命就不长了。意思是五色固然不应当枯槁，但如果五色的精华全部发散于外表，而体内没有蓄积，也不是好现象。大抵观察五色之中，必须以明润为主，而在明润之中，必须含有蕴蓄之气，如果一概将光华发散于外表，也是凶兆。观察面色的奥妙，大概就在于此了。
经文说：五色的诊断主要看明堂。明堂，指鼻子。所以鼻头颜色发青的，腹中疼痛；微微发黑的，体内有痰饮；黄色的，属于湿热；白色的，属于气虚；赤色的，属于肺热；明亮的，表示没有疾病。如果伤寒病人鼻孔干燥，这是邪热在阳明经肌肉之间的表现，时间久了必将发生鼻衄（鼻出血）。病人想打喷嚏却打不出来的，是寒证。鼻塞且流出浊涕的，是风热证。呼吸时伴有鼾声嗜睡的，是风温证。鼻孔干燥，颜色黑如烟煤的，是阳毒热邪深重的表现。鼻孔呼出冷气，湿润且发黑的，是阴毒冷极的表现。凡是在患病过程中，鼻子变黑如煤炭一样，是大凶的征兆。如果见到鼻孔煽动张合，是肺气即将断绝的证候。凡是产妇鼻部出现黑气，或者流鼻血的，是胃气败坏、肺气断绝的危重征候，古代方剂用二味参苏饮加附子来抢救，大多能存活。
The *Huangdi Neijing* (Yellow Emperor's Inner Canon) states: "Pulse changes correspond to the moon, and complexion changes correspond to the sun." Complexion is what can be easily seen with the naked eye. For instance, in Wind Injury (Shangfeng, an exogenous wind pathogen invasion), the Que-Ting area (the glabella and upper nasal bridge) must be lustrous and bright; in Cold Damage (Shanghan, an exogenous cold pathogen invasion), the Que-Ting area must be dim and dull. A cyan or black facial color indicates Cold syndrome or a Direct Transmission to Yin meridians (Zhizhong Yinzheng). A purple or red facial color indicates Heat syndrome or a Transmitted Interior Syndrome (Chuanjing Lizheng). If, after sweating therapy, the facial redness remains prominent, this indicates that the exterior pathogen has not been thoroughly expelled, and one should reapply exterior-releasing methods. Furthermore, if excessive Yin cold repels Yang Qi, causing the entire face to turn red, this is a sign of Floating Yang (Daiyang), and urgent warming therapy should be applied to unblock Yang Qi. Generally, the appearance of black color portends bad luck and indicates the most severe illness, whereas the appearance of yellow color portends good luck, meaning that even if the illness is severe, it is treatable. The classics state: "A yellow face with cyan eyes, a yellow face with red eyes, a yellow face with white eyes, and a yellow face with black eyes are all auspicious." This is because yellow belongs to Earth; although evil symptoms are present, the Earth element (representing Spleen/Stomach Qi) has not yet perished, so rescue is possible. However, a cyan face with red eyes, a red face with white eyes, a cyan face with black eyes, a black face with white eyes, and a red face with cyan eyes are all difficult to treat, indicating that without the Earth color, the Stomach Qi has perished. In areas such as the Tian-Ting (forehead), Yin-Tang (between the eyebrows), and Nian-Shou (root to tip of the nose), dry and withered black color is ominous, while bright and moist yellow color is auspicious. However, the five colors in humans cannot be perfectly equal. The classics state: "The five colors are the splendor of Qi." Red should resemble white silk wrapping cinnabar (Baiguo Zhu), appearing contained and lustrous, not like hematite (Zhe); white should resemble goose feathers (Eyu), appearing fine and pure, not like salt (Yan); green/cyan should resemble the luster of dark jade (Cangbi), appearing moist and glossy, not like indigo dye (Lan); yellow should resemble raw realgar (Xionghuang) wrapped in silk (Luo), appearing soft and bright, not like loess soil (Huangtu); black should resemble heavy lacquer (Chongqi), appearing deep and shiny, not like earthy grey minerals (Dicang). The "desired" qualities of the five colors all seek moisture and luster, while the "undesired" qualities all abhor dryness and withering. The classics further state: "If the subtle images of the five colors appear fully exposed, the person's lifespan will not be long." This means that while the five colors should not be dry and withered, if the essence and brilliance of the five colors are entirely exhausted and projected outward, with no accumulation within, this is also unfavorable. Generally, among the five colors, brightness and moisture are paramount, but within this brightness and moisture, there must be a sense of containment. If the radiance is uniformly projected outward without restraint, it is also an ominous sign. The subtlety of observing complexion lies precisely in this.
The classics state: "The judgment of the five colors depends on the Ming-Tang." The Ming-Tang refers to the nose. Therefore, if the tip of the nose is cyan, there is abdominal pain; if slightly black, there is Phlegm-Fluid retention (Tanyin); if yellow, it indicates Damp-Heat (Shi-Re); if white, it indicates Qi Deficiency (Qixu); if red, it indicates Lung Heat (Feire); if bright and clear, it indicates health. If a patient with Cold Damage has dry nostrils, this indicates that evil heat is in the muscles of the Yangming channel, and prolonged stagnation will inevitably lead to Epistaxis (Nuxue). If a patient desires to sneeze but cannot, it indicates Cold. Nasal congestion with turbid discharge indicates Wind-Heat (Feng-Re). Snoring during sleep indicates Wind-Warmth (Fengwen). Dry nostrils with a black color resembling coal smoke indicate Deep Heat from Yang Toxin (Yangdu). Nostrils exhaling cold air, appearing moist and black, indicate Extreme Cold from Yin Toxin (Yindu). Generally, if the nose turns black like coal during an illness, it is a major ominous sign. If nasal flaring is observed, it is a sign that Lung Qi is about to perish. If a postpartum woman exhibits black qi around the nose or suffers from epistaxis, it is a critical sign of Stomach failure and Lung exhaustion. Ancient formulas used Erwei Renshen Su Yin (Two-Ingredient Ginseng and Perilla Decoction) added with Fuzi (Prepared Aconite Root) for rescue, and many survived.