To enhance image security in transmission and storage, we proposed a new color image encryption approach based on orthogonal Lagrange-Fourier moments (OLFMs) and a 6D fractional-order chaotic system (6D-FCS), in which the complex dynamic behavior of 6D-FCS is leveraged to generate highly unpredictable key streams, thereby ensuring strong confusion and diffusion properties. The proposed encryption algorithm comprised two stages: First, the 6D-FCS was employed to generate chaotic sequences that shuffle pixel positions, establishing the confusion stage and ensuring a high level of pixel scrambling. Second, OLFMs were used to modify pixel values, thereby achieving the diffusion stage. The numerical simulations and security analysis showed that the proposed encryption algorithm provides a key space greater than 2⁶⁴⁷, indicating strong security and outstanding encryption performance, as evidenced by key space, correlation coefficient, information entropy, histogram, UACI, and NPCR, thereby resisting statistical, differential, noise, and cropping attacks, highlighting its efficacy for image encryption. Moreover, the proposed encryption algorithm exhibits significant security and superiority to the related algorithms.