夫色之同于众人者。气候之常。而不同于众人者。赋禀之变。故夫气质不齐。形色亦异。经曰。木形之人青。
土形之人黄。火形之人赤。金形之人白。水形之人黑。盖其赋禀独盛。故其气色独着也。然五形之人。其脏
腑之盛衰。骨节之大小。筋之粗细。肉之坚脆。皮之浓薄。血之清浊。气之滑涩。脉之长短。血之多少。经络之
数。营卫之度。又各不齐。扩而充之。则人心之不同。如其面焉。岂仅阴阳五人。五五二十五人而已哉。变化
盖无穷矣。是故圣人视其颜色。黄赤者多热气。青白者少热气。黑色者多血少气。参之四时。合之五行。可
以推其生克。断其吉凶矣。四诊心法云。五脏之色。随五形发见。百岁不变者。主色也。四时之色。随四时加
临。推迁不常者。客色也。主色人气之所生。客色岁气之所化。岁气胜人气为顺。人气胜岁气为逆。所谓逆
者。春当青而反白。秋当白而反赤。夏当赤而反黑。冬当黑而反黄。长夏当黄而反青。可随时而观也。夫色
之生于心也。体天地。法四时。则阴阳。顺人情。岂特一端而已哉。夫各有所当也。
夫色之不能一致者。气质之变也。而亦有老少之殊。方其少也。血气盛。肌肉滑。气道通。营卫之行速。及其
老也。血气衰。肌肉枯。气道涩。营卫之行迟。夫是故老者之色多憔悴。少者之色多润泽也。经曰。人生十岁。
五脏始定。血气已通。其气在下。故好走。二十岁。血气始盛。肌肉方长。故好趋。三十岁。五脏大定。肌肉坚固。
血脉盛满。故好步。四十岁。五脏六腑十二经脉皆大盛。已平定。腠理始疏。荣华颓落。发颇斑白。平盛不摇。
故好坐。五十岁肝气始衰。肝叶始薄。胆汁始减。目始不明。六十岁。心气始衰。善忧悲。血气懈惰。故好卧。七
十岁。脾气虚。皮肤枯。八十岁。肺气衰。魂魄离。故言善误。九十岁。肾气焦。四脏经脉空虚。百岁。五脏皆虚。神
气皆去。形骸独居而终矣。盖五十以前。五脏相生而日长。五十而后。五脏相减而日消。此天年之常也。然
有年已老而体未衰者。有年方壮而形先槁者。虽强弱之不齐。亦盛衰之各异尔。要之盛于中者。必着于
外。衰于里者。必形于表。故望其形色之盛衰。即可知其脏腑之盛衰。脏腑形色。犹根本之与枝叶也。此老
少之同异。可一隅而反三也。
面色与常人相同者，是气候的正常表现；而与常人不同者，则是先天禀赋的变异。因此，人的气质各不相同，形色也随之而异。《内经》说：木形之人面色青，土形之人面色黄，火形之人面色赤，金形之人面色白，水形之人面色黑。这是因为他们的禀赋中某一行特别旺盛，所以其气色也特别显著。然而，五形之人，其脏腑的盛衰、骨节的大小、筋脉的粗细、肌肉的坚脆、皮肤的厚薄、血液的清浊、气的滑涩、脉搏的长短、血液的多少、经络的数量、营卫的度数，又各自不同。推而广之，人心性不同，就像他们的面容一样，哪里仅仅是阴阳五人、五五二十五种类型而已呢？变化可以说是无穷无尽的。
因此，圣人观察人的面色：面色黄赤的多为热气盛，面色青白的多为热气少，面色黑的多血少气。结合四时气候变化，配合五行生克理论，可以推断其相生相克的关系，判断吉凶祸福。《四诊心法》说：五脏的面色，随着五形之人显现出来，终身不变的是主色（本来的面色）；随四季气候变化而改变，推移不固定的，是客色（暂时的气色）。主色由人气所生，客色由岁气所化。岁气胜过人气为顺，人气胜过岁气为逆。所谓的“逆”，是指春天应当面色青却反见白色，秋天应当面色白却反见红色，夏天应当面色赤却反见黑色，冬天应当面色黑却反见黄色，长夏应当面色黄却反见青色。这可以随时观察来判断。
面色的产生源于心，体察天地之道，效法四时规律，顺应阴阳变化，合乎人情事理，岂止是一个方面那么简单呢？各有所当的道理。
面色不能保持一致，是因为气质的变化。而且也有老年和少年的区别。在年少时，血气旺盛，肌肉滑润，气道通畅，营卫运行迅速；到了年老时，血气衰退，肌肉枯槁，气道涩滞，营卫运行迟缓。因此，老年人的面色多憔悴，年轻人的面色多润泽。《内经》说：人十岁时，五脏始定，血气已通，气机下行，所以喜欢跑动；二十岁时，血气开始旺盛，肌肉正在生长，所以喜欢快走；三十岁时，五脏大定，肌肉坚固，血脉盛满，所以喜欢步行；四十岁时，五脏六腑及十二经脉都盛大且平稳，腠理开始疏松，荣华衰落，头发开始斑白，平盛不再摇动，所以喜欢静坐；五十岁时，肝气开始衰退，肝叶变薄，胆汁减少，眼睛开始不明亮；六十岁时，心气开始衰退，容易忧愁悲伤，血气懈怠懒惰，所以喜欢躺卧；七十岁时，脾气虚弱，皮肤枯槁；八十岁时，肺气衰退，魂魄离散，所以说话容易出错；九十岁时，肾气枯竭，四脏经脉空虚；百岁之时，五脏皆虚，神气离去，只剩形骸独自存在而终老。大概五十岁以前，五脏相生而日益生长；五十岁以后，五脏相减而日益消损。这是天年正常的规律。
然而，有的人年纪老了身体却没有衰退，有的人年纪正壮形体却先枯槁。虽然强弱不齐，也是盛衰各异罢了。总之，内部旺盛的，必然表现在外部；内部衰弱的，必然显露于体表。所以观察其形色的盛衰，就可以知道脏腑的盛衰。脏腑与形色，就像根本与枝叶的关系一样。关于老少同异的知识，可以由此举一反三。
Complexions that are the same as those of the general population represent normal climatic conditions, while those that differ from the general population represent variations in innate constitution (Bianfu). Therefore, since human constitutions vary, their physical forms and complexions also differ. The Classics state: Individuals with Wood-type constitution have a green complexion; Earth-type individuals have a yellow complexion; Fire-type individuals have a red complexion; Metal-type individuals have a white complexion; Water-type individuals have a black complexion. This is because one aspect of their innate constitution is particularly dominant, so their Qi and color appear especially distinct. However, among the five types, the prosperity or decline of Zang-Fu organs, the size of bones and joints, the thickness or thinness of tendons, the firmness or fragility of muscles, the thickness or thinness of skin, the clarity or turbidity of Blood, the smoothness or stagnation of Qi, the length or shortness of pulses, the quantity of Blood, the number of meridians, and the regulation of Ying and Wei (Nutritive and Defensive Qi) all vary individually. Expanding upon this, human minds differ just as their faces do; it is not limited to merely the Yin-Yang five types and the twenty-five resulting combinations. Changes are essentially infinite.
Thus, sages observe colors: Yellowish-red complexions indicate abundant Heat-Qi; bluish-white complexions indicate scarce Heat-Qi; black complexions indicate abundant Blood but deficient Qi. By correlating these with the Four Seasons and integrating them with the Five Elements, one can deduce generating and overcoming relationships, thereby judging auspiciousness and inauspiciousness. *Sizhen Xinfa* states: The colors of the Five Zang organs manifest according to the five constitutional types. Colors that remain unchanged throughout a hundred years are called Principal Colors (Zhuse); colors that change with the Four Seasons and shift irregularly are called Guest Colors (Kese). Principal Colors are generated by individual Qi, while Guest Colors are transformed by Annual Qi. When Annual Qi overcomes Individual Qi, it is considered favorable (Shun); when Individual Qi overcomes Annual Qi, it is considered unfavorable (Ni). "Unfavorable" refers to situations such as spring expecting green but seeing white, autumn expecting white but seeing red, summer expecting red but seeing black, winter expecting black but seeing yellow, and late summer expecting yellow but seeing green. These can be observed at any time.
The generation of complexion originates from the Heart; it embodies the Way of Heaven and Earth, models the Four Seasons, follows Yin-Yang, and conforms to human nature. It is certainly not limited to a single aspect. Each has its appropriate principle.
The inability of complexions to remain uniform is due to changes in constitution. Furthermore, there are distinctions between the young and the old. In youth, Blood and Qi are abundant, muscles are supple, Qi channels are unobstructed, and the movement of Ying and Wei is rapid. In old age, Blood and Qi decline, muscles become withered, Qi channels become stagnant, and the movement of Ying and Wei becomes slow. Therefore, the complexions of the elderly are often haggard, while those of the young are often lustrous. The Classics state: At ten years of age, the Five Zang organs begin to stabilize, Blood and Qi circulate, and Qi moves downward, so they enjoy running. At twenty years of age, Blood and Qi begin to flourish, muscles are growing, so they enjoy brisk walking. At thirty years of age, the Five Zang organs are fully established, muscles are firm, and blood vessels are full, so they enjoy walking. At forty years of age, the Five Zang, Six Fu, and Twelve Meridians are in peak condition and stable; the interstices begin to loosen, radiance declines, hair begins to gray, and stability prevails without agitation, so they enjoy sitting. At fifty years of age, Liver Qi begins to decline, the liver lobes thin, bile decreases, and vision begins to dim. At sixty years of age, Heart Qi begins to decline, leading to sorrow and grief, Blood and Qi become sluggish, so they enjoy lying down. At seventy years of age, Spleen Qi is deficient, and skin becomes withered. At eighty years of age, Lung Qi declines, Hun and Po separate, causing speech errors. At ninety years of age, Kidney Qi is exhausted, and the meridians of the Four Zang organs are empty. At one hundred years of age, all Five Zang organs are deficient, Shen-Qi departs, leaving only the physical form to conclude life. Generally, before fifty, the Five Zang generate each other and grow daily; after fifty, they diminish sequentially and decline daily. This is the normal course of the natural lifespan.
However, some who are old show no physical decline, while some who are young appear prematurely withered. Although strength and weakness vary, prosperity and decline differ accordingly. Ultimately, what is prosperous internally must manifest externally; what is deficient internally must appear on the surface. Thus, by observing the prosperity or decline of physical form and complexion, one can know the prosperity or decline of the Zang-Fu organs. Zang-Fu organs and physical form/complexion are like roots and branches. From the similarities and differences between the young and the old, one can infer other cases by analogy.