既讲春夏秋冬之异。须知昼夜阴晴之殊。盖人在气交之中。与气候之相应也。犹影之随身。犹水之鉴形。
夫是故昼为阳。卫气日行于阳。夜为阴。卫气夜行于阴。天温日阳。则人血淖溢而卫气浮。天寒日阴。则人
血凝泣而卫气沉。血气营卫之相应如此。则色之相应可征矣。何者。脉以应月。色以应日。昼则气行于阳。
色之见也。当光辉而外映。夜则气行于阴。色之见也。当明润而内含。晴则气热。热则气淖泽。淖泽则黄赤。
阴则气寒。寒则血凝泣。凝泣则青黑。此皆其应也。色之应乎昼夜阴晴者。常也。不应乎昼夜阴晴者。病也。
夫百病多以旦慧、昼安、夕加、夜甚。色当因病之旦慧、昼安、夕加、夜甚也。其或暮轻朝重。夜减昼加。则不在
乎卫气。而独主乎脏气矣。是必以脏气之所不胜时者甚。以其所胜时者起。夫所不胜者。克我者也。所胜
者。我克者也。盖以一日分为四时。以四时分应五脏。肝日甲乙。其时寅卯。心日丙丁。其时巳午。肺日庚辛。
其时申酉。肾日壬癸。其时亥子。脾日戊己。其时辰戌丑未。以五脏之日时。合五脏之病色。其生克之理。间
甚之候。死生之期。胥于是乎推。亦于是乎断矣。然而一日之内。一时之间。寒暄不齐。雨 靡定。则又各有
所胜。各有所不胜矣。若夫宫室有冷暖之殊。衣服有寒温之异。病或因之而重轻。色或因之而损益。虽不
当以昼夜论。亦皆可作阴晴观。触目关心。存乎人矣。
既然已经论述了春、夏、秋、冬四季的差异，就必须知晓昼、夜、阴、晴的不同。因为人处于天地气交之中，与气候的变化是相应的。这就像影子跟随身体一样，又像水面映照形体一样。
因此，白天属阳，卫气在白天运行于体表（阳分）；夜晚属阴，卫气在夜晚运行于体内（阴分）。天气温暖且阳光充足时，人的血液流动滑利充盈，卫气浮越于外；天气寒冷且阴暗时，人的血液凝涩不畅，卫气沉伏于内。血气与营卫的相应关系就是这样，那么面色随其变化的规律也是可以验证的了。为什么呢？脉象应合月亮的盈亏变化，面色应合太阳的昼夜变化。白天阳气行于体表，面色的显现应当光辉明亮而外露；夜晚阳气行于体内，面色的显现应当明润光泽而内含。晴天则气温热，热则气机滑利润泽，气机滑利润泽则面色呈现黄赤色；阴天则气温寒，寒则血液凝涩，血液凝涩则面色呈现青黑色。这些都是相应的表现。面色顺应昼夜阴晴变化的，是正常的；不顺应昼夜阴晴变化的，就是病态。
各种疾病大多表现为早晨神志清醒、白天安宁、傍晚加重、夜间剧烈。面色也应当随着疾病的“晨慧、昼安、夕加、夜甚”而变化。如果有的病人傍晚轻、早晨重，夜间减轻、白天加重，这就不是由卫气的运行规律主导，而是单独由脏气的盛衰主导了。这一定是因为遇到克制本脏的气时病情加重，遇到被本脏克制的气时病情好转。所谓“所不胜”，就是克制我的五行之气；所谓“所胜”，就是我克制的五行之气。大概将一天分为四个时段，以这四个时段对应五脏。肝对应甲乙日，时辰为寅、卯；心对应丙丁日，时辰为巳、午；肺对应庚辛日，时辰为申、酉；肾对应壬癸日，时辰为亥、子；脾对应戊己日，时辰为辰、戌、丑、未。将五脏对应的日子和时辰，结合五脏病变的面色，其中的生克原理、病情间歇与加重的征候、以及生死预后的期限，都据此推演，也据此判断。
然而，一天之内，一个时辰之间，冷暖不均，雨势不定，则又各有胜负、各有所不胜的情况。至于宫室有冷暖的区别，衣服有寒温的差异，病情可能因此而有轻重变化，面色也可能因此而有增减改变。虽然不能单纯用昼夜来论断，但也都可以当作阴晴来看待。这一切都需要观察者触目留心，存乎于心罢了。
Having discussed the differences among Spring, Summer, Autumn, and Winter, one must also understand the distinctions of Day, Night, Clear weather, and Overcast weather. This is because humans exist within the intersection of Heaven and Earth Qi (vital energy), responding to climatic changes. It is like a shadow following the body, or like water reflecting a form.
Therefore, Day belongs to Yang, during which Wei Qi (Defensive Qi) circulates in the Yang aspects (exterior/body surface) by day; Night belongs to Yin, during which Wei Qi circulates in the Yin aspects (interior/organs) by night. When the weather is warm and sunny, human blood flows smoothly and abundantly, and Wei Qi floats outward; when the weather is cold and overcast, human blood becomes sluggish and congealed, and Wei Qi sinks inward. Such is the correspondence between Blood-Qi and Ying-Wei (Nutritive and Defensive Qi). Thus, the corresponding changes in facial complexion can be verified. Why? Because Pulse corresponds to the waxing and waning of the Moon, while Complexion corresponds to the Sun’s day and night cycle. During the day, Qi moves in the Yang aspects; thus, the manifestation of complexion should be radiant and externally visible. At night, Qi moves in the Yin aspects; thus, the manifestation of complexion should be bright, moist, and internally contained. On clear days, the Qi is warm; warmth makes Qi smooth and lubricated; smoothness and lubrication result in a yellowish-red complexion. On overcast days, the Qi is cold; cold causes blood to congeal and become sluggish; congestion and slowness result in a bluish-black complexion. These are all instances of such correspondence. A complexion that responds to day/night and clear/overcast conditions is normal; one that does not respond is pathological.
Most diseases manifest as: lucid in the morning, peaceful during the day, aggravated in the evening, and severe at night. The complexion should accordingly reflect this pattern of "morning lucidity, daytime peace, evening aggravation, nighttime severity." However, if a patient is lighter in the evening and heavier in the morning, or less severe at night and more severe during the day, this is not governed by the circulation of Wei Qi, but solely by the state of Zang Qi (Visceral Qi). In such cases, the disease worsens when encountering the element that conquers it (the "unconquered" or "so bu sheng") and improves when encountering the element it conquers (the "conquered" or "so sheng"). The "unconquered" refers to what conquers me; the "conquered" refers to what I conquer. Generally, a day is divided into four periods, corresponding to the Five Zang Organs. The Liver corresponds to Jia-Yi days, with hours Yin-Mao; the Heart corresponds to Bing-Ding days, with hours Si-Wu; the Lungs correspond to Geng-Xin days, with hours Shen-You; the Kidneys correspond to Ren-Gui days, with hours Hai-Zi; the Spleen corresponds to Wu-Ji days, with hours Chen-Xu-Chou-Wei. By combining the days and hours of the Five Zang Organs with the pathological complexions of these organs, one can deduce the principles of generation and conquest, observe the patterns of remission and exacerbation, and determine the timing of death or survival. All reasoning and judgment are derived from this.
Nevertheless, within a single day or even a single two-hour period, temperature and humidity may vary unevenly, and rain may fall unpredictably, leading to varying degrees of dominance and subordination among climatic factors. Furthermore, residences differ in warmth and coolness, and clothing varies in thermal properties. Illness may therefore become heavier or lighter, and complexion may increase or decrease due to these factors. Although these cannot be judged solely by day/night cycles, they can all be viewed through the lens of clear/overcast conditions. Ultimately, this requires the observer to pay close attention and keep these observations in mind.