This article examines why brush and ink (bimo), the core formal language of Chinese ink painting, remains essential to heavy-color (zhongcai) mountain and water painting, where colour composition might seem to make it secondary. The author approaches the question from two angles: historical development and cultural symbolism. Historically, early blue-green painting relied on outline and colour filling with little texturing; the axe-cut cun strokes associated with Li Sixun and Li Zhaodao marked the entry of brushwork as a modelling method and aesthetic standard. From the mid-Tang onwards, with Wang Wei’s claim that ink painting is supreme and the critical judgements of Jing Hao, Shen Hao, Wang Yuanqi and Tang Dai, colour was progressively subordinated to ink. In the 1980s, the influence of Japanese mineral-pigment painting led some painters to weaken or abandon ink, but the ensuing debate reaffirmed brush and ink as the bottom line of Chinese painting, as seen in Zhuo Hejun, Xu Jun, Fang Xiang, Xue Liang, Yang Xianshun and Qi Enjin. Drawing on Cassirer and Langer, the author argues that brush and ink is a cultural symbol embodying Daoist aesthetics and the painter’s cultural identity.