The mood of an image is typically conveyed by the combination of colors. Such a combination of colors is called a color theme. In this paper, we propose a color transformation method based on color theme that can i) control the ratios of assigned colors while ii) maintaining the spatial coherence of regions. In our color transformation method, one color in a color theme is assigned to the pixels in an image and the pixels are transformed toward the corresponding color. We consider the color assignment problem as a labeling problem. To ensure that i) and ii) above can be achieved, we introduce offsets that are added to labeling costs in the label optimization process. The offsets are determined according to the concept of maximally stable extremal regions (MSER) in order to preserve spatial coherence. Experimental results show that our approach is effective for the control of the color ratios and preserving the coherence of the regions.