Computer-Assisted Auto Coloring (CAAC) has great potential in terms of lowering production cost and saving time in cel animation production. In this paper, a novel approach to automatically color the animation character of line drawings based on region matching and master frames is proposed. Firstly, some important attributes of a region such as curve length, character points, area etc. are investigated. Then, based on these attributes, a detailed process of region matching is presented followed by the coloring process. The results show that our approach can straightforwardly handle most cases, hence the aim of saving time and labor is realized.