In this paper we propose a color decomposition method for multicolor printing of watercolors including areas overlapping each print layer. Watercolors have an important feature that the observed colors are different by the printing order. This method is based on a particle density model for expressing the effects of watercolors. The approach of this method is to solve an inverse problem, that is, determining a printed area corresponding to a watercolor from an observed image. Our purpose in this study is to estimate woodblocks from a woodblock print. We focus on multicolor woodblock prints such as Ukiyo-e: Japanese traditional woodblock printing. The results of woodblock estimation will be utilized to preserve techniques and prints of Ukiyo-e. An Ukiyo-e print is created from several woodblocks with several watercolors, and has a mixing color expression similar to the effects of watercolor painting.