Because quaternion representation is able to preserve the relationship among RGB channels of a color image, we take advantage of this characteristic and propose a new color image denoising method, named the Quaternion Adaptive Non-local Coupled Means (QANLCM). QANLCM first builds a four-variable optimization model by decomposing the original noisy image into a luminance component and a chromaticity component, and then alternatively updates the four variables in each denoising iteration. Simulations and comparisons demonstrate that QANLCM shows a superiority to other non-local means methods in removing Gaussian noise from color images.