Bamboo’s single color and susceptibility to mold substantially limit its wide application. Therefore, dyeing and mold prevention have become pivotal technologies for the high-value-added utilization of bamboo. This study selected the extracts of three plants (Caesalpinia sappan L. (Cs), Rubia cordifolia L. (Rc), and Carthamus tinctorius L. (Ct)) for dyeing and mold prevention experiments. The results showed that the three extracts had good dyeing effects on bamboo, with total color differences (ΔE*) of 31.69, 21.61, and 32.29 compared to untreated bamboo, respectively. Additionally, these had a moderate inhibitory effect on mold. The introduction of metal mordants effectively enhances the dyeing effect of plant dyes and the effectiveness of mold inhibition. Through the joint modification of Cs and Cu, the color fixation rate increased from 3.12% to 9.20% compared with the Cs extract. A Cu 1 g:300 mL Cs extract impregnation of bamboo can completely inhibit the growth of Aspergillus niger, and a 1 g:1100 mL ratio can completely inhibit the growth of Trichoderma viride. This study provides a new concept for applying plant dyes in the dyeing and mold prevention treatment of bamboo. The dual-effect treatment of dyeing and mold prevention enhances the visual characteristics of bamboo while imparting it with good mold prevention performance.