As one of the earliest forms of painting in human history, ancient murals are invaluable cultural treasures. They reflect scientific, technological, artistic, and societal developments from different eras, holding immense historical and artistic value. Murals evolved from simple patterns to complex, colorful representations of inner emotions and aspirations, and they provide essential visual evidence for understanding ancient cultures. The use of color in murals also expresses ethnic identity, religious beliefs, social customs, and aesthetic preferences. Pigments are central to mural production. In ancient times, pigments were sourced from natural minerals (e.g., earth red, malachite green), synthetic minerals (e.g., minium, ultramarine), and plant extracts (e.g., indigo, rattan yellow). Among these, inorganic mineral pigments were widely used. However, some mineral pigments—especially lead-based ones—have deteriorated over time, showing discoloration or blackening. Lead-based pigments were historically favored for their vivid hues. Minium (lead tetraoxide, Pb₃O₄) was among the earliest synthetic pigments, though its color could be influenced by impurities from high-temperature preparation. It is unstable compared to natural mineral pigments. Micro- and non-destructive testing methods have revealed minium use in various cultural relics, many of which have since discolored. This discoloration is primarily due to reactions forming black lead dioxide (β-PbO₂) or lead sulfide (PbS). Another lead pigment, lead white, composed of Pb₃(OH)₂(CO₃)₂ or PbCO₃ are more susceptible to H₂S to produce PbS. The discoloration of lead-based pigments is easily affected by light, humidity, microorganisms, and other factors such as acidity-alkalinity and soluble salts of the mural surface. This paper summarizes the relevant physical, chemical, and biological discoloration mechanisms of pigments as follows:1) electron holes are able to be formed inside the pigment after long-term absorption of ultraviolet light energy so that photochemical reactions occur and the valence state change (e.g., Pb₃O₄→PbO₂ or Pb₃O₄→Pb²⁺); 2) the combination of higher humidity and pollution gas creates an acidic environment, causing the released H⁺ to destroy the ionic bond of Pb—O and triggering the disproportionation reaction, which result in the transformation of Pb₃O₄ to PbO₂; 3) microorganisms can quickly grow under suitable temperature and humidity on the mural surface (on the one hand, organic acids and peroxides produced by microbial metabolism can react with pigments, leading to fading or blackening particularly in lead-based pigments; on the other hand, pigments may be absorbed into microbial cells and react with their secretions, altering the microbes’ color, and as these pigmented cells accumulate on the mural surface, they cause further discoloration). To recreate the original appearance of ancient murals, pigment color restoration techniques are essential. High-energy laser technology has emerged as a promising method for this purpose and is becoming a key focus in the field, offering significant potential for future applications. In addition, this article briefly introduces other pigments such as red pigments cinnabar and earth red, green pigments atacamite and Paris green, and blue pigments lapis lazuli and azurite, and briefly summarizes the relevant fading principles and causes, and proposes that environmental quality has a close relationship with maintaining the color of pigments. Therefore, it is of great significance to the long-term preservation of murals to comprehensively monitor the environment, reduce the air pollution, improve the environmental quality, deepen the research on the mechanism of microbial actions on mural pigments, and carry out disease control. Recent conservation strategies for cultural relics in China have shifted from purely remedial efforts to including both remedial and preventive measures. This study aims to provide a scientific basis for understanding pigment discoloration and to guide effective conservation to slow down the discoloration of ancient murals.