Peirce was a man of obsessions. And, although his whole style of thinking and writing was non-systematic, it was never erratic, as it has sometimes been argued. Fundamentally it was obsessive, and only apparently diffuse and disperse. His enormous curiosity often leads us astray. But, no matter how esoteric or capricious his interest may appear, his work always sheds an unexpected light on some basic and enduring issues. The synthetical dimension of reasoning is one of them. Another, closely linked to it, is the issue of vision and color.